Update to Zig 0.16.0

This commit represents the majority of the work necessary to upgrade
Ghostty to use Zig 0.16.0.

Key parts:

* In addition to its previous responsibilities, the global state now
  houses state for global I/O implementations and the process
  environment. It is now also utilized in the main application along
  with the C library. Where necessary, global state is isolated from key
  parts of the implementation (e.g., in libghostty subsystems), and it's
  expected that this list will grow.

* We currently manage our own C translation layer where necessary. In
  these cases, cImport has been removed in favor of the new external
  translate-c package. Due to fixes that have needed be made to properly
  translate the dependencies that were swapped out, as mentioned, we
  have had to backport fixes from the current translate-c package (and
  the upstream Arocc dependency). We will host this ourselves until Zig
  0.17.0 is released with these fixes.

* Where necessary (only a small number of cases), some stdlib code from
  0.15.2 (and even from 0.17.0) has been taken, adopted, and vendored in
  lib/compat.

Co-authored-by: Leah Amelia Chen <hi@pluie.me>

src/helpgen.zig

@@ -7,12 +7,9 @@ const Config = @import("config/Config.zig");
 const Action = @import("cli/ghostty.zig").Action;
 const KeybindAction = @import("input/Binding.zig").Action;
 
-pub fn main() !void {
-    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
-    const alloc = gpa.allocator();
-
+pub fn main(init: std.process.Init) !void {
     var buf: [4096]u8 = undefined;
-    var stdout = std.fs.File.stdout().writerStreaming(&buf);
+    var stdout = std.Io.File.stdout().writerStreaming(init.io, &buf);
     const writer = &stdout.interface;
     try writer.writeAll(
         \\// THIS FILE IS AUTO GENERATED
@@ -20,6 +17,7 @@ pub fn main() !void {
         \\
     );
 
+    const alloc = init.arena.allocator();
     try genConfig(alloc, writer);
     try genActions(alloc, writer);
     try genKeybindActions(alloc, writer);