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/instance.zig

@@ -0,0 +1,61 @@
+const ChainedStruct = @import("types.zig").ChainedStruct;
+const RequestAdapterStatus = @import("types.zig").RequestAdapterStatus;
+const Surface = @import("surface.zig").Surface;
+const Adapter = @import("adapter.zig").Adapter;
+const RequestAdapterOptions = @import("types.zig").RequestAdapterOptions;
+const RequestAdapterCallback = @import("callbacks.zig").RequestAdapterCallback;
+const Impl = @import("interface.zig").Impl;
+const dawn = @import("dawn.zig");
+
+pub const Instance = opaque {
+    pub const Descriptor = extern struct {
+        pub const NextInChain = extern union {
+            generic: ?*const ChainedStruct,
+            dawn_instance_descriptor: *const dawn.InstanceDescriptor,
+        };
+
+        next_in_chain: NextInChain = .{ .generic = null },
+    };
+
+    pub inline fn createSurface(instance: *Instance, descriptor: *const Surface.Descriptor) *Surface {
+        return Impl.instanceCreateSurface(instance, descriptor);
+    }
+
+    pub inline fn requestAdapter(
+        instance: *Instance,
+        options: ?*const RequestAdapterOptions,
+        context: anytype,
+        comptime callback: fn (
+            ctx: @TypeOf(context),
+            status: RequestAdapterStatus,
+            adapter: *Adapter,
+            message: ?[*:0]const u8,
+        ) callconv(.Inline) void,
+    ) void {
+        const Context = @TypeOf(context);
+        const Helper = struct {
+            pub fn cCallback(
+                status: RequestAdapterStatus,
+                adapter: *Adapter,
+                message: ?[*:0]const u8,
+                userdata: ?*anyopaque,
+            ) callconv(.C) void {
+                callback(
+                    if (Context == void) {} else @ptrCast(Context, @alignCast(@alignOf(Context), userdata)),
+                    status,
+                    adapter,
+                    message,
+                );
+            }
+        };
+        Impl.instanceRequestAdapter(instance, options, Helper.cCallback, if (Context == void) null else context);
+    }
+
+    pub inline fn reference(instance: *Instance) void {
+        Impl.instanceReference(instance);
+    }
+
+    pub inline fn release(instance: *Instance) void {
+        Impl.instanceRelease(instance);
+    }
+};