Add opacity support to LS and compiler

[dabbott]

What

Support generating components with opacity.

A few quirks/limitations:

• Opacity should be between 0 and 1. However, the LS number picker doesn't work very well with decimals at the moment. First type the number, e.g. "3", then type the "." in front of it
• NSBox doesn't support rendering with alphaValue on macOS, and alphaValue doesn't affect subviews. We can work around this but it'll be more effort. Consider MultipliedAlphaProviding and MultipliedAlphaConsuming protocols.

Testing Plan

• Tested this change locally
• Checked that existing features work

[lonabot]

	1 Warning
⚠️	Big PR, try to keep changes smaller if you can

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