…multiple overloads.

Always clear errors before trying automatic coercion for a new compound expression overload.

Remove use of QString from non-ICU Qt stub bidi implementation since we weren't making use of it.

Add support for `MGL_FUNCTION('format', <text>, <options dictionary>)`

- No dedicated support for creating format expressions
- Java accessors for 'text-field' flatten back to String
- 'text-field' setter implicitly creates a 'format' expression. For tests, use JsonArray to build an equivalent format expression by hand.

- Port of arabic.test.js from mapbox-gl-rtl-text
- Modify BiDi::getLine to remove trailing nulls in the event UBIDI_REMOVE_BIDI_CONTROLS causes the string to shorten.
- Patch vendored ICU to avoid undefined undefined bit shifting behavior (triggered sanitizer failure)