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/surface.zig

@@ -0,0 +1,72 @@
+const ChainedStruct = @import("types.zig").ChainedStruct;
+const Impl = @import("interface.zig").Impl;
+
+pub const Surface = opaque {
+    pub const Descriptor = extern struct {
+        pub const NextInChain = extern union {
+            generic: ?*const ChainedStruct,
+            from_android_native_window: *const DescriptorFromAndroidNativeWindow,
+            from_canvas_html_selector: *const DescriptorFromCanvasHTMLSelector,
+            from_metal_layer: *const DescriptorFromMetalLayer,
+            from_wayland_surface: *const DescriptorFromWaylandSurface,
+            from_windows_core_window: *const DescriptorFromWindowsCoreWindow,
+            from_windows_hwnd: *const DescriptorFromWindowsHWND,
+            from_windows_swap_chain_panel: *const DescriptorFromWindowsSwapChainPanel,
+            from_xlib_window: *const DescriptorFromXlibWindow,
+        };
+
+        next_in_chain: NextInChain = .{ .generic = null },
+        label: ?[*:0]const u8 = null,
+    };
+
+    pub const DescriptorFromAndroidNativeWindow = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_android_native_window },
+        window: *anyopaque,
+    };
+
+    pub const DescriptorFromCanvasHTMLSelector = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_canvas_html_selector },
+        selector: [*:0]const u8,
+    };
+
+    pub const DescriptorFromMetalLayer = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_metal_layer },
+        layer: *anyopaque,
+    };
+
+    pub const DescriptorFromWaylandSurface = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_wayland_surface },
+        display: *anyopaque,
+        surface: *anyopaque,
+    };
+
+    pub const DescriptorFromWindowsCoreWindow = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_windows_core_window },
+        core_window: *anyopaque,
+    };
+
+    pub const DescriptorFromWindowsHWND = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_windows_hwnd },
+        hinstance: *anyopaque,
+        hwnd: *anyopaque,
+    };
+
+    pub const DescriptorFromWindowsSwapChainPanel = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_windows_swap_chain_panel },
+        swap_chain_panel: *anyopaque,
+    };
+
+    pub const DescriptorFromXlibWindow = extern struct {
+        chain: ChainedStruct = .{ .next = null, .s_type = .surface_descriptor_from_xlib_window },
+        display: *anyopaque,
+        window: u32,
+    };
+
+    pub inline fn reference(surface: *Surface) void {
+        Impl.surfaceReference(surface);
+    }
+
+    pub inline fn release(surface: *Surface) void {
+        Impl.surfaceRelease(surface);
+    }
+};