Never resolve tokens after evaluating a text-field or icon-image expression

[anandthakker]

GL Native quivalent of mapbox/mapbox-gl-js#5599

[anandthakker]

I think this will be much cleaner to implement once basic SDK support is in place, because at that point, we can likely remove the {Camera,Source,Composite}Function<T> templates (or at least their corresponding *Stops<T> members), making the function => expression conversion code much more tightly contained.

Since resolving this issue amounts to adding token string => ["concat", ...] to that conversion, it will be a simpler and cleaner change at that point than it would be now.

[1ec5]

Fixed in #11509.