Support expressions in filters

[anandthakker]

Closes #4077
Closes #4410

• Converts classic filters to expressions under the hood
• Also accepts {expression: [...]}, requiring that the given
  expression be of type Boolean
• Benchmark to assess performance impact acainst classic filters
• Add fixtures for validation.test.js
• Manually test debug page
• Add some kind of partial string matching? ( Add expression operator testing a string against a regular expression #4089 / Add expression operator testing whether a string contains a substring #4113 )

cc @jfirebaugh @aparlato

[indus]

Will there be an expression for "object.hasOwnProperty()" or "array.indexOf() != -1". I'm living with a patched version since #4490

[anandthakker]

@indus Good question - there is a ["has", "propertyName"] expression (see #4777), but we should also add [ "contains" , ... ] for checking presence in an array.

[anandthakker]

@aparlato @nickidlugash updated with:

• support for [zoom]
• [contains]

Still working on performance but it should be usable for developing styles.

[anandthakker]

Rebased onto master and reworked to take advantage of #5234 -- performance is much better, but evaluation performance is still about 8x compared to non-expressions-based filters:

And creation performance is much slower:

[anandthakker]

Along the lines of #5379 , @mourner suggests leaving the existing filter implementation in place, and making expressions support additive / opt-in.

[anandthakker]

Back to being a bit worse after rebasing onto the recent updates on master (no-eval, etc.):

Bench	master	expressions-filter	gist
FilterCreate	0.303 ms	9.81 ms ( +9.51 ms / 15.1 std devs )	https://bl.ocks.org/anonymous/raw/f98f920d15e3df367eb5175987548939/
FilterEvaluate	0.136 ms	2.93 ms ( +2.79 ms / 37.3 std devs )	https://bl.ocks.org/anonymous/raw/b42d635f2eda75b0627f95801985d7ba/

[anandthakker]

cc @mourner @jfirebaugh I was hoping the recent changes would mean we could stick with converting old-style filters, but looks like we should drop the conversion for now.

[jfirebaugh]

https://github.com/mapbox/mapbox-gl-js/compare/expressions-filter-perf gets it down to 3.5-4x slower.

[jfirebaugh]

I merged the alternative without conversion, #5434. We'll hopefully be resurrecting the conversion code from this PR at some point, but closing for now.