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>

example/zig-vt/src/main.zig

@@ -1,26 +1,20 @@
 const std = @import("std");
 const ghostty_vt = @import("ghostty-vt");
 
-pub fn main() !void {
-    // Use a debug allocator so we get leak checking. You probably want
-    // to replace this for release builds.
-    var gpa: std.heap.DebugAllocator(.{}) = .init;
-    defer _ = gpa.deinit();
-    const alloc = gpa.allocator();
-
+pub fn main(init: std.process.Init) !void {
     // Initialize a terminal.
-    var t: ghostty_vt.Terminal = try .init(alloc, .{
+    var t: ghostty_vt.Terminal = try .init(init.io, init.gpa, .{
         .cols = 6,
         .rows = 40,
     });
-    defer t.deinit(alloc);
+    defer t.deinit(init.gpa);
 
     // Write some text. It'll wrap because this is too long for our
     // columns size above (6).
     try t.printString("Hello, World!");
 
     // Get the plain string view of the terminal screen.
-    const str = try t.plainString(alloc);
-    defer alloc.free(str);
+    const str = try t.plainString(init.gpa);
+    defer init.gpa.free(str);
     std.debug.print("{s}\n", .{str});
 }