fix(typescript-estree): support private optional property definition

[sosukesuzuki]

Supports private optional property definition

[typescript-eslint]

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[nx-cloud]

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CI ran the following commands for commit 8b58782. Click to see the status, the terminal output, and the build insights.

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	Node 12.x - nx test @typescript-eslint/eslint-plugin-internal
	Node 12.x - nx test @typescript-eslint/eslint-plugin-tslint
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[codecov]

Codecov Report

Merging #3997 (8b58782) into master (41d6cac) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3997      +/-   ##
==========================================
- Coverage   93.40%   93.38%   -0.02%     
==========================================
  Files         151      168      +17     
  Lines        8093     9506    +1413     
  Branches     2568     2943     +375     
==========================================
+ Hits         7559     8877    +1318     
- Misses        181      237      +56     
- Partials      353      392      +39     

Flag	Coverage Δ
unittest	93.38% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/typescript-estree/src/convert.ts	98.28% <ø> (ø)
packages/typescript-estree/src/ts-estree/index.ts	100.00% <0.00%> (ø)
...escript-estree/src/semantic-or-syntactic-errors.ts	87.50% <0.00%> (ø)
...-estree/src/create-program/createProjectProgram.ts	94.11% <0.00%> (ø)
packages/typescript-estree/src/convert-comments.ts	100.00% <0.00%> (ø)
...ckages/typescript-estree/src/jsx/xhtml-entities.ts	100.00% <0.00%> (ø)
packages/typescript-estree/src/node-utils.ts	97.83% <0.00%> (ø)
packages/typescript-estree/src/ast-converter.ts	100.00% <0.00%> (ø)
...ript-estree/src/create-program/createSourceFile.ts	87.50% <0.00%> (ø)
packages/typescript-estree/src/version-check.ts	100.00% <0.00%> (ø)
... and 8 more

[JoshuaKGoldberg]

LGTM, thanks for taking this on @sosukesuzuki! Just requesting a couple more test cases to make sure it works well with different optional initial values.

[JoshuaKGoldberg]

By the way -- most PRs generally are asked to correspond to an existing issue to make make sure the change is something that would be accepted before you spend too much time working on it. This one is a definite win IMO, so just a heads up for next time. 🙂

(echoing from the other thread for visibility)

[bradzacher]

noice - thanks for fixing this!