Publish Flow type definitions alongside compiled bundle

[anandthakker]

There isn't currently a straightforward way for a downstream consumer of Mapbox GL JS to benefit from the Flow type annotations that exist throughout our source code (and, specifically, on our public API). We should find a way to distribute dist/mapbox-gl.js.flow alongside the main bundle.

facebook/flow#5871 suggests that the flow gen-flow-types tool may get deprecated soon and so we probably don't want to rely on that.

Since we do include src/ in our npm package, we could use the approach mentioned in facebook/flow#5871 (comment) -- i.e., have dist/mapbox-gl.js.flow look like:

// @flow
export * from '../src/index.js';

This almost works, except that the downstream package would need to add many of the ignores that we use:

mapbox-gl-js/.flowconfig

Lines 2 to 12 in f55e548

	.*/node_modules/@mapbox/jsonlint-lines-primitives/.*
	.*/node_modules/stylelint/.*
	.*/node_modules/unflowify/.*
	.*/node_modules/flow-coverage-report/.*
	.*/node_modules/babel-plugin-transform-react-remove-prop-types/.*
	.*/node_modules/conventional-changelog-core/.*
	.*/node_modules/htmltojsx/.*
	.*/node_modules/documentation/.*
	.*/node_modules/module-deps/.*
	.*/test/unit/style-spec/fixture/invalidjson.input.json
	.*/test/integration/render-tests/.*

[shanshanzhu]

Can you try this in the .flowconfig? <PROJECT_ROOT>/node_modules/.*