macOS: Implement maximize config (works for GTK)

[mitchellh]

Discussed in #5881

^{Originally posted by taylrfnt February 19, 2025}
Porting over from Discord...

Issue Details

When using the maximize configuration option, the Ghostty window is not drawn to the maximized size (see recording below) as expected.

Reproduction Steps

1. Create a minimal Ghostty config of maximize = true
2. Restart Ghostty (super+q)
3. Open a new Ghostty window, observe it is not maximized.

Ghostty Configuration

maximize = true

Update Channel

tip

Ghostty Version

Ghostty 1.1.3-main+da32534e

Version
  - version: 1.1.3-main+da32534e
  - channel: tip
Build Config
  - Zig version: 0.13.0
  - build mode : builtin.OptimizeMode.ReleaseFast
  - app runtime: apprt.Runtime.none
  - font engine: font.main.Backend.coretext
  - renderer   : renderer.Metal
  - libxev     : main.Backend.kqueue

[!NOTE]
This might be tangentially related to #5783, but it seemed distinct enough (different configuration options) to warrant its own Discussion item.