all: move standalone libraries to libs/ subdirectory

The root dir of our repository has grown quite a lot the past few months.

I'd like to make it more clear where the bulk of the engine lives (`src/`) and
also make it more clear which Mach libraries are consumable as standalone projects.

As for the name of this directory, `libs` was my first choice but there's a bit of
a convention of that being external libraries in Zig projects _today_, while these
are libraries maintained as part of Mach in this repository - not external ones.

We will name this directory `libs`, and if we have a need for external libraries
we will use `external` or `deps` for that directory name. I considered other names
such as `components`, `systems`, `modules` (which are bad as they overlap with
major ECS / engine concepts), and it seems likely the official Zig package manager
will break the convention of using a `libs` dir anyway.

Performed via:

```sh
mkdir libs/
git mv freetype libs/
git mv basisu libs/
git mv gamemode libs/
git mv glfw libs/
git mv gpu libs/
git mv gpu-dawn libs/
git mv sysaudio libs/
git mv sysjs libs/
git mv ecs libs/
```

git-subtree-dir: glfw
git-subtree-mainline: 0d5b853443
git-subtree-split: 572d1144f11b353abdb64fff828b25a4f0fbb7ca

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

git mv ecs libs/

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

libs/glfw/.github/FUNDING.yml

@@ -0,0 +1 @@
+github: slimsag

libs/glfw/.github/pull_request_template.md

@@ -0,0 +1,5 @@
+Please send your change to [the main repository](https://github.com/hexops/mach/tree/main/glfw) instead, sorry for the trouble!
+
+This helps us avoid some complex merge conflicts we run into when changes are made to both repositories and history needs to be reconciled. Keeping PRs in just that repository enables us to use `git subtree` to trivially keep the two repositories in sync.
+
+Once your PR is merged over there, it'll automatically sync to this repository.

libs/glfw/.github/workflows/ci.yml

@@ -0,0 +1,91 @@
+name: CI
+on:
+  - push
+  - pull_request
+jobs:
+  x86_64-linux:
+    runs-on: ubuntu-latest
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run by the push
+    # to the branch.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
+    env:
+      DISPLAY: ':99.0'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Zig
+        run: |
+          sudo apt install xz-utils
+          sudo sh -c 'wget -c https://ziglang.org/builds/zig-linux-x86_64-0.10.0-dev.3551+92568a009.tar.xz -O - | tar -xJ --strip-components=1 -C /usr/local/bin'
+      - name: x86_64-linux -> x86_64-macos
+        run: zig build test -Dtarget=x86_64-macos
+        env:
+          AGREE: true
+      - name: x86_64-linux -> aarch64-macos
+        run: zig build test -Dtarget=aarch64-macos
+        env:
+          AGREE: true
+      - name: x86_64-linux -> x86_64-windows
+        run: zig build test -Dtarget=x86_64-windows
+      - name: launch xvfb
+        run: Xvfb :99 -screen 0 1680x720x24 > /dev/null 2>&1 &
+      - name: test
+        run: |
+          sudo add-apt-repository -y ppa:kisak/kisak-mesa
+          sudo apt-get update
+          sudo apt-get install mesa-utils mesa-utils-extra mesa-va-drivers mesa-vdpau-drivers mesa-vulkan-drivers xvfb
+          zig build test
+  x86_64-windows:
+    runs-on: windows-latest
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run by the push
+    # to the branch.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install Git
+        run: choco install git
+      - name: Setup Zig
+        run: |
+          $ProgressPreference = 'SilentlyContinue'
+          Invoke-WebRequest -Uri "https://ziglang.org/builds/zig-windows-x86_64-0.10.0-dev.3551+92568a009.zip" -OutFile "C:\zig.zip"
+          cd C:\
+          7z x zig.zip
+          Add-Content $env:GITHUB_PATH "C:\zig-windows-x86_64-0.10.0-dev.3551+92568a009\"
+      - name: x86_64-windows -> x86_64-macos
+        run: zig build test -Dtarget=x86_64-macos
+        env:
+          AGREE: true
+      - name: x86_64-windows -> aarch64-macos
+        run: zig build test -Dtarget=aarch64-macos
+        env:
+          AGREE: true
+      - name: x86_64-windows -> x86_64-linux
+        run: zig build test -Dtarget=x86_64-linux
+      - name: test
+        run: zig build test
+  x86_64-macos:
+    runs-on: macos-12
+    # We want to run on external PRs, but not on our own internal PRs as they'll be run by the push
+    # to the branch.
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Zig
+        run: |
+          brew uninstall --ignore-dependencies libx11 # https://github.com/ziglang/zig/issues/11066
+          brew install xz
+          sudo sh -c 'wget -c https://ziglang.org/builds/zig-macos-x86_64-0.10.0-dev.3551+92568a009.tar.xz -O - | tar -xJ --strip-components=1 -C /usr/local/bin'
+      - name: test
+        run: zig build test
+        env:
+          AGREE: true
+      - name: x86_64-macos -> aarch64-macos
+        run: zig build test -Dtarget=aarch64-macos
+        env:
+          AGREE: true
+      - name: x86_64-macos -> x86_64-windows
+        run: zig build test -Dtarget=x86_64-windows
+      - name: x86_64-macos -> x86_64-linux
+        run: zig build test -Dtarget=x86_64-linux

libs/glfw/.github/workflows/m1_ci.yml

@@ -0,0 +1,39 @@
+name: M1
+on:
+  # SECURITY: This must be a push event only, otherwise our M1 mac runner would be compromised by
+  # third-party pull requests which could run arbitrary code. This way, we can restrict it to
+  # collaborators of the repository only.
+  #
+  # Whenever GitHub Actions gets official M1 support, we can use that for PRs and get rid of this
+  # self-hosted runner: https://github.com/actions/virtual-environments/issues/2187 
+  - push
+jobs:
+  aarch64-macos:
+    if: ${{ github.repository == 'hexops/mach-glfw' }}
+    runs-on: [self-hosted, macOS, ARM64]
+    defaults:
+      run:
+        shell: "/usr/bin/arch -arch arm64e /bin/bash --noprofile --norc -eo pipefail {0}"
+    steps:
+      - name: Clean repository submodules
+        # See https://github.com/actions/checkout/issues/385
+        run: |
+          rm -rf $GITHUB_WORKSPACE && mkdir $GITHUB_WORKSPACE
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Zig
+        run: |
+          sudo rm -rf /usr/local/bin/zig /usr/local/bin/lib/
+          sudo sh -c 'wget -c https://ziglang.org/builds/zig-macos-aarch64-0.10.0-dev.3551+92568a009.tar.xz -O - | tar -xJ --strip-components=1 -C /usr/local/bin'
+      - name: test
+        run: zig build test
+        env:
+          AGREE: true
+      - name: aarch64-macos -> x86_64-macos
+        run: zig build test -Dtarget=x86_64-macos
+        env:
+          AGREE: true
+      - name: aarch64-macos -> x86_64-windows
+        run: zig build test -Dtarget=x86_64-windows
+      - name: aarch64-macos -> x86_64-linux
+        run: zig build test -Dtarget=x86_64-linux