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/src/mod.zig

@@ -0,0 +1,167 @@
+//! Modifier key flags
+//!
+//! See glfw.setKeyCallback for how these are used.
+
+const c = @import("c.zig").c;
+
+// must be in sync with GLFW C constants in modifier group, search for "@defgroup mods Modifier key flags"
+/// A bitmask of all key modifiers
+pub const Mods = packed struct {
+    shift: bool = false,
+    control: bool = false,
+    alt: bool = false,
+    super: bool = false,
+    caps_lock: bool = false,
+    num_lock: bool = false,
+    _reserved: u2 = 0,
+
+    inline fn verifyIntType(comptime IntType: type) void {
+        comptime {
+            switch (@typeInfo(IntType)) {
+                .Int => {},
+                else => @compileError("Int was not of int type"),
+            }
+        }
+    }
+
+    pub inline fn toInt(self: Mods, comptime IntType: type) IntType {
+        verifyIntType(IntType);
+        return @intCast(IntType, @bitCast(u8, self));
+    }
+
+    pub inline fn fromInt(flags: anytype) Mods {
+        verifyIntType(@TypeOf(flags));
+        return @bitCast(Mods, @intCast(u8, flags));
+    }
+};
+
+/// Holds all GLFW mod values in their raw form.
+pub const RawMods = struct {
+    /// If this bit is set one or more Shift keys were held down.
+    pub const shift = c.GLFW_MOD_SHIFT;
+
+    /// If this bit is set one or more Control keys were held down.
+    pub const control = c.GLFW_MOD_CONTROL;
+
+    /// If this bit is set one or more Alt keys were held down.
+    pub const alt = c.GLFW_MOD_ALT;
+
+    /// If this bit is set one or more Super keys were held down.
+    pub const super = c.GLFW_MOD_SUPER;
+
+    /// If this bit is set the Caps Lock key is enabled and the glfw.lock_key_mods input mode is set.
+    pub const caps_lock = c.GLFW_MOD_CAPS_LOCK;
+
+    /// If this bit is set the Num Lock key is enabled and the glfw.lock_key_mods input mode is set.
+    pub const num_lock = c.GLFW_MOD_NUM_LOCK;
+};
+
+test "shift int to bitmask" {
+    const std = @import("std");
+
+    const int_mod = RawMods.shift;
+    const mod = Mods.fromInt(int_mod);
+
+    try std.testing.expect(mod.shift == true);
+    try std.testing.expect(mod.control == false);
+    try std.testing.expect(mod.alt == false);
+    try std.testing.expect(mod.super == false);
+    try std.testing.expect(mod.caps_lock == false);
+    try std.testing.expect(mod.num_lock == false);
+}
+
+test "shift int and alt to bitmask" {
+    const std = @import("std");
+
+    const int_mod = RawMods.shift | RawMods.alt;
+    const mod = Mods.fromInt(int_mod);
+
+    try std.testing.expect(mod.shift == true);
+    try std.testing.expect(mod.control == false);
+    try std.testing.expect(mod.alt == true);
+    try std.testing.expect(mod.super == false);
+    try std.testing.expect(mod.caps_lock == false);
+    try std.testing.expect(mod.num_lock == false);
+}
+
+test "super int to bitmask" {
+    const std = @import("std");
+
+    const int_mod = RawMods.super;
+    const mod = Mods.fromInt(int_mod);
+
+    try std.testing.expect(mod.shift == false);
+    try std.testing.expect(mod.control == false);
+    try std.testing.expect(mod.alt == false);
+    try std.testing.expect(mod.super == true);
+    try std.testing.expect(mod.caps_lock == false);
+    try std.testing.expect(mod.num_lock == false);
+}
+
+test "num lock int to bitmask" {
+    const std = @import("std");
+
+    const int_mod = RawMods.num_lock;
+    const mod = Mods.fromInt(int_mod);
+
+    try std.testing.expect(mod.shift == false);
+    try std.testing.expect(mod.control == false);
+    try std.testing.expect(mod.alt == false);
+    try std.testing.expect(mod.super == false);
+    try std.testing.expect(mod.caps_lock == false);
+    try std.testing.expect(mod.num_lock == true);
+}
+
+test "all int to bitmask" {
+    const std = @import("std");
+
+    const int_mod = RawMods.shift | RawMods.control |
+        RawMods.alt | RawMods.super |
+        RawMods.caps_lock | RawMods.num_lock;
+    const mod = Mods.fromInt(int_mod);
+
+    try std.testing.expect(mod.shift == true);
+    try std.testing.expect(mod.control == true);
+    try std.testing.expect(mod.alt == true);
+    try std.testing.expect(mod.super == true);
+    try std.testing.expect(mod.caps_lock == true);
+    try std.testing.expect(mod.num_lock == true);
+}
+
+test "shift bitmask to int" {
+    const std = @import("std");
+
+    const mod = Mods{ .shift = true };
+    const int_mod = mod.toInt(c_int);
+
+    try std.testing.expectEqual(int_mod, RawMods.shift);
+}
+
+test "shift and alt bitmask to int" {
+    const std = @import("std");
+
+    const mod = Mods{ .shift = true, .alt = true };
+    const int_mod = mod.toInt(c_int);
+
+    try std.testing.expectEqual(int_mod, RawMods.shift | RawMods.alt);
+}
+
+test "all bitmask to int" {
+    const std = @import("std");
+
+    const mod = Mods{
+        .shift = true,
+        .control = true,
+        .alt = true,
+        .super = true,
+        .caps_lock = true,
+        .num_lock = true,
+    };
+    const int_mod = mod.toInt(c_int);
+
+    const expected = RawMods.shift | RawMods.control |
+        RawMods.alt | RawMods.super |
+        RawMods.caps_lock | RawMods.num_lock;
+
+    try std.testing.expectEqual(int_mod, expected);
+}