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>

test/fuzz-libghostty/src/fuzz_stream.zig

@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("std");
 const ghostty_vt = @import("ghostty-vt");
 const mem = @import("mem.zig");
@@ -24,9 +25,23 @@ pub export fn zig_fuzz_test(
     const alloc = fuzz_alloc.allocator();
     const input = buf[0..len];
 
+    const argv0 = "ghostty-fuzz";
+    const argv0_windows = argv0_windows: {
+        var argv0_windows_buf: [std.unicode.calcUtf16LeLen(argv0) catch unreachable]u16 = undefined;
+        _ = std.unicode.utf8ToUtf16Le(&argv0_windows_buf, argv0) catch unreachable;
+        break :argv0_windows argv0_windows_buf;
+    };
+    var threaded: std.Io.Threaded = .init(alloc, .{
+        .argv0 = .init(.{ .vector = if (builtin.target.os.tag == .windows)
+            &argv0_windows
+        else
+            &.{argv0} }),
+    });
+    defer threaded.deinit();
+
     // Allocate a terminal; if we run out of fixed-buffer space just
     // skip this input (not a bug, just a very large allocation).
-    var t = Terminal.init(alloc, .{
+    var t = Terminal.init(threaded.io(), alloc, .{
         .cols = 80,
         .rows = 24,
         .max_scrollback = 100,