macOS: Fix center window with fixed bounds size

[Quadriphobs1]

This PR fixes window showing up in the center of the monitor when center: true option is provided.

The idea is to set the window_wize when creating the window using native_window.initWithContentRect_styleMask_backing_defer_screen_()

Before:

After:

Release Notes:

• N/A

[ConradIrwin]

Thanks for this! I accidentally broke this a while back.

Can you please run cargo fmt on your code to keep the linter happy, then I will merge.

[Quadriphobs1]

Thanks for taking a look.

I have run cargo fmt and push the changes, can you confirm if there is anymore lint error.

[ConradIrwin]

Looks good, thanks!