Mouse pointer should not be hidden in letterbox/pillarbox area of display

[sh95014]

To Reproduce
Steps to reproduce the behavior:

1. Launch Mariani
2. Drag the main window so that it's not the correct aspect ratio for the Apple II screen.
3. Move mouse over the excess area inside the window but outside the emulated screen.

Expected behavior
Mouse pointer should be visible.

Actual behavior
Mouse pointer is not visible.

Versions (please complete the following information):

• OS: macOS 12.2.1
• Mariani: 7c36741

Additional context
Needs some math that corresponds to the MTLTexture layout in EmulatorRenderer.m to exclude the letterbox/pillarbox areas from the tracking area computation in EmulatorView.mm.