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/gpu/src/dawn.zig

@@ -0,0 +1,59 @@
+const ChainedStruct = @import("types.zig").ChainedStruct;
+const Texture = @import("texture.zig").Texture;
+pub const Interface = @import("dawn_impl.zig").Interface;
+
+pub const CacheDeviceDescriptor = extern struct {
+    chain: ChainedStruct = .{ .next = null, .s_type = .dawn_cache_device_descriptor },
+    isolation_key: [*:0]const u8 = "",
+};
+
+pub const EncoderInternalUsageDescriptor = extern struct {
+    chain: ChainedStruct = .{ .next = null, .s_type = .dawn_encoder_internal_usage_descriptor },
+    use_internal_usages: bool = false,
+};
+
+pub const InstanceDescriptor = extern struct {
+    chain: ChainedStruct = .{ .next = null, .s_type = .dawn_instance_descriptor },
+    additional_runtime_search_paths_count: u32 = 0,
+    additional_runtime_search_paths: ?[*]const u8 = null,
+
+    /// Provides a slightly friendlier Zig API to initialize this structure.
+    pub inline fn init(v: struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .dawn_instance_descriptor },
+        additional_runtime_search_paths: ?[]const u8 = null,
+    }) InstanceDescriptor {
+        return .{
+            .chain = v.chain,
+            .additional_runtime_search_paths_count = if (v.additional_runtime_search_paths) |e| @intCast(u32, e.len) else 0,
+            .additional_runtime_search_paths = if (v.additional_runtime_search_paths) |e| e.ptr else null,
+        };
+    }
+};
+
+pub const TextureInternalUsageDescriptor = extern struct {
+    chain: ChainedStruct = .{ .next = null, .s_type = .dawn_texture_internal_usage_descriptor },
+    internal_usage: Texture.UsageFlags = Texture.UsageFlags.none,
+};
+
+pub const TogglesDeviceDescriptor = extern struct {
+    chain: ChainedStruct = .{ .next = null, .s_type = .dawn_toggles_device_descriptor },
+    force_enabled_toggles_count: u32 = 0,
+    force_enabled_toggles: ?[*]const u8 = null,
+    force_disabled_toggles_count: u32 = 0,
+    force_disabled_toggles: ?[*]const u8 = null,
+
+    /// Provides a slightly friendlier Zig API to initialize this structure.
+    pub inline fn init(v: struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .dawn_toggles_device_descriptor },
+        force_enabled_toggles: ?[]const u8 = null,
+        force_disabled_toggles: ?[]const u8 = null,
+    }) TogglesDeviceDescriptor {
+        return .{
+            .chain = v.chain,
+            .force_enabled_toggles_count = if (v.force_enabled_toggles) |e| @intCast(u32, e.len) else 0,
+            .force_enabled_toggles = if (v.force_enabled_toggles) |e| e.ptr else null,
+            .force_disabled_toggles_count = if (v.force_disabled_toggles) |e| @intCast(u32, e.len) else 0,
+            .force_disabled_toggles = if (v.force_disabled_toggles) |e| e.ptr else null,
+        };
+    }
+};