* [core] Bump gl-js version
* [core] Implement image expression
* [core] Use new image expression
* [core] Coerce image expression to / from string
* [core] Serialize evaluated image
* [core] Pass available images to layout
* [core] Pass images to evaluation context
* [core] Set available flag value based on image availability
* [core] Allow image coercion to boolean to indicate image availability
* [core] Coalesce image expression
* [core] Add image expression to next build system
* [core] Align serialization format and evaluated type with gl-js
* [core] Add images to expression evaluation method
* [core] Add support for Image expression to expression test runner
* [core] Unskip image expression tests
* [core] Update unit tests
* [core] Use image expression in annotation manager
* [core] Add string to ImageExpression conversion
* [core] Add image expression to expression dsl
* [core] Convert tokens for implicitly created Image literal
* [core] Fix clang format
* [core] Split generated style code lines that are over 120 characters
* [core] Add unit test for image expression equality
* [core] Add image property expression evaluation unit test
* [core] Unskip image expression render test
* [core] Skip 'in' expression tests
* [core] Ignore fill-pattern/update-feature-state render test
* [core] Rename Image::serialize to Image::toValue
The output of Layer::getProperty is a mapbox::base::Value which is
equivalent to JSON. When setting the value of an enum property via JSON
its value would be a string, so it would be natural to return a string
too.
Also, the numbers generated depend on the enum definition. They are not
part of the style spec.
