Add support for titlebar options in `config.window_frame` on macos

[Jay-Madden]

Is your feature request related to a problem? Please describe.
The default titlebar on wezterm is a bit of an eyesore compared to other programs that have a customized titlebar that matches the background. E.G ITerm2

Describe the solution you'd like

Wezterm exposes config.window_frame https://wezfurlong.org/wezterm/config/lua/config/window_frame.html as an option, primarily for wayland systems. I am proposing that the titlebar options be extended to work on macos as well.

Options to be supported:

  inactive_titlebar_bg = '#353535',
  active_titlebar_bg = '#2b2042',
  inactive_titlebar_fg = '#cccccc',
  active_titlebar_fg = '#ffffff',
  inactive_titlebar_border_bottom = '#2b2042',
  active_titlebar_border_bottom = '#2b2042',

Implementation

The NSView container for the titlebar can found with the className NSTitlebarContainerView next to the window view in the view tree. This view can be used to render the title bar however you want.

Describe alternatives you've considered
N/a

Additional context

Screenshot of ITerm2 with nicer titlebar

[basus]

I currently hide the titlebar because it looks kinda ugly on macOS. I'd love to have this so Wezterm fits in better with the rest of the UI.

[Jay-Madden]

I've opened #6558 to support matching the background to the theme color. Supporting all the other Wayland options i believe is possible but likely not too useful to the majority of people. Just matching the background goes a long way.