Make Expressions fully deserializable

[anandthakker]

Currently, CompoundExpression#_evaluate doesn't survive serialization/deserialization via our web worker transfer scheme:

mapbox-gl-js/src/util/web_worker_transfer.js

Line 101 in f87d7e3

register('CompoundExpression', CompoundExpression, {omit: ['_evaluate']});

This was fine until now, because we only evaluate a {Source,Composite}Binder's expression on the worker side, during populatePaintArray

mapbox-gl-js/src/data/program_configuration.js

Line 139 in f87d7e3

const value = this.expression.evaluate({zoom: 0}, feature);

For #6020, however, we'll need to evaluate again on the main thread when making updates, and so we should refactor CompoundExpression so that it can be fully rehydrated on the main thread.

[anandthakker]

cc @asheemmamoowala

[jfirebaugh]

It would be great if we could use this as an opportunity to refactor/untangle the following types:

• Expression
• StyleExpression
• StyleExpressionWithErrorHandling
• ZoomConstantExpression
• ZoomDependentExpression
• ConstantExpression
• SourceExpression
• CameraExpression
• CompositeExpression
• StylePropertyExpression
• StylePropertyFunction

That seems like more types than is ideal.

[anandthakker]

The performance considerations in #6367 suggest that we might want to solve this another way.