Fix format expression options validation

[ahk]

This branch fixes format expression options validation. Previously any value literals used within fields of the options object would fail to validate, causing the style to fail to run. This solution chooses to recursively unbundle fields of options objects. Unbundling is an operation that coerces new Object(...) constructed primitives (String, Boolean, Number) into bare primitives. This makes little difference except to all our internal runtime type reflection during validation.

Closes #8271

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
• tagged @mapbox/studio and/or @mapbox/maps-design if this PR includes style spec changes
• tagged @mapbox/gl-native if this PR includes shader changes or needs a native port

[ahk]

Potentially we'd also like to pick up the missing web documentation for format expression options here. If anyone knows that we already documented the options but they got lost (gl-native and gl-js are feature split on text-color right now) I would be happy to be pointed to the documentation text to include in this fix.

[asheemmamoowala]

This is looking good. Could use a couple additional test cases for a format expression with a text-font override, and with invalid values or invalid overrides