patches/helium: macOS UI transparency/ vibrancy

[sameerasw]

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This PR adds support for macOS UI transparency for the browser with vibrancy utilizing NSVisualEffect.

Initial plan for the implementation

1. Initialize vibrancy with fixed transparency
2. Fix bugs and glitches which can occur (overlay UI elements, rounded corners ...)
3. Give user a control to adjust the transparency amount
4. Testing

Some early implementation screenshots:

Notice in the light theme, the transparency is barely noticeable. This is due to how the NSVisualEffects behave and out of our control.