[mapbox-gl] allow SymbolLayout.symbol-sort-key to be an Expression

[dmytro-gokun]

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes: https://docs.mapbox.com/mapbox-gl-js/style-spec/layers/#layout-symbol-symbol-sort-key
• Include tests for your changes

[typescript-bot]

@dmytro-gokun Thank you for submitting this PR!

🔔 @dobrud @PatrickR @macobo @LiamAttClarke @life777 @mklopets @amxfonseca - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[typescript-bot]

Since you're a listed owner and the build passed, this PR is fast-tracked. A maintainer will merge shortly. If it shouldn't be merged yet, please leave a comment saying so and we'll wait. Thank you for your contribution to DefinitelyTyped!

[typescript-bot]

👋 Hi there! I’ve run some quick measurements against master and your PR. These metrics should help the humans reviewing this PR gauge whether it might negatively affect compile times or editor responsiveness for users who install these typings.

Let’s review the numbers, shall we?

Comparison details 📊

	master	#44076	diff
Batch compilation
Memory usage (MiB)	88.3	86.5	-2.1%
Type count	12344	12344	0%
Assignability cache size	35145	35145	0%
Language service
Samples taken	2252	2254	0%
Identifiers in tests	2252	2254	0%
getCompletionsAtPosition
Mean duration (ms)	355.9	357.6	+0.5%
Mean CV	9.2%	8.8%
Worst duration (ms)	483.0	488.3	+1.1%
Worst identifier	document	document
getQuickInfoAtPosition
Mean duration (ms)	346.1	348.4	+0.7%
Mean CV	9.1%	8.7%	-4.1%
Worst duration (ms)	465.1	482.4	+3.7%
Worst identifier	querySelector	originalEvent

It looks like nothing changed too much. I won’t post performance data again unless it gets worse.

[typescript-bot]

I just published @types/mapbox-gl@1.9.1 to npm.