feat(typescript-estree): support for parsing 3.7 features

[bradzacher]

Fixes #1033 (this doesn't add support for them in rules).

The AST I've gone with here is the same as the one babel (and flow) uses.
It looks like there is still an open question within ESTree itself whether or not it's the right direction to go in: estree/estree#146

Lacking a better option, I figured this was a good AST rep to go with.

[typescript-eslint]

Thanks for the PR, @bradzacher!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[JamesHenry]

I added to the README to clarify that we will not look to support pre-releases if doing so does not negatively impact the support for the latest stable version

[codecov]

Codecov Report

Merging #1045 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1045      +/-   ##
==========================================
+ Coverage   94.01%   94.06%   +0.04%     
==========================================
  Files         115      115              
  Lines        5064     5086      +22     
  Branches     1416     1423       +7     
==========================================
+ Hits         4761     4784      +23     
+ Misses        175      174       -1     
  Partials      128      128

Impacted Files	Coverage Δ
...t-plugin/src/rules/adjacent-overload-signatures.ts	93.02% <ø> (+2.11%)	⬆️
packages/parser/src/visitor-keys.ts	100% <ø> (ø)	⬆️
packages/eslint-plugin/src/rules/indent.ts	92.3% <ø> (ø)	⬆️
packages/typescript-estree/src/node-utils.ts	97.72% <100%> (ø)	⬆️
packages/typescript-estree/src/convert.ts	98.99% <100%> (+0.03%)	⬆️
packages/typescript-estree/src/parser.ts	91.89% <100%> (ø)	⬆️
...ackages/eslint-plugin/src/rules/prefer-readonly.ts	99.1% <100%> (ø)	⬆️
.../typescript-estree/src/ts-estree/ast-node-types.ts	100% <100%> (ø)	⬆️

[JamesHenry]

@bradzacher FYI still failing on unit tests

[bradzacher]

Yeah there's something weird with ts-jest, composite projects and ts 3.7.
I reprod it locally once, then when I ran the failing test individually it went away completely.

Ill take another look.

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edit: it stopped reproing locally because of the jest cache, running yarn test --no-cache revealed the error consistently.

I don't know why running the test individually "fixed" it. Running without the cache repros when running individually or as a batch.

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edit: It seems like 3.7 is stricter with composite projects and project configs, so TS was erroring when the tests attempted to require a .ts file across the boundary.