fix(eslint-plugin): false-positive/negative with array index in no-unnecessary-condition

[ypresto]

This PR fixes several false-positive/negatives in no-unnecessary-condition.

• False-positive at nullish coalescing after array index access: arr[42]?.foo ?? 0
• False-negative at arr[42] ?? 0 where arr[42] is always nullish or never.
• False-negative at arr[0].foo?.bar where foo is not nullable.

[typescript-eslint]

Thanks for the PR, @ypresto!

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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[nx-cloud]

Nx Cloud Report

CI ran the following commands for commit caf350e. Click to see the status, the terminal output, and the build insights.

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Status	Command
	nx test @typescript-eslint/eslint-plugin-internal
	nx test @typescript-eslint/eslint-plugin-tslint
	nx test @typescript-eslint/eslint-plugin-tslint
	nx test @typescript-eslint/eslint-plugin
	nx test @typescript-eslint/eslint-plugin
	nx test @typescript-eslint/eslint-plugin-tslint
	nx test @typescript-eslint/eslint-plugin
	nx run-many --target=typecheck --all --parallel
	nx test @typescript-eslint/parser
	nx test @typescript-eslint/experimental-utils
	nx test @typescript-eslint/scope-manager
	nx test @typescript-eslint/visitor-keys
	nx test @typescript-eslint/typescript-estree
	nx run-many --target=build --all --parallel
	nx test @typescript-eslint/parser
	nx test @typescript-eslint/experimental-utils
	nx run-many --target=build --all --parallel
	nx test @typescript-eslint/scope-manager
	nx test @typescript-eslint/visitor-keys
	nx test @typescript-eslint/typescript-estree

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[codecov]

Codecov Report

Merging #3805 (caf350e) into master (055add0) will increase coverage by 0.89%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3805      +/-   ##
==========================================
+ Coverage   92.68%   93.57%   +0.89%     
==========================================
  Files         327      147     -180     
  Lines       11351     7865    -3486     
  Branches     3201     2492     -709     
==========================================
- Hits        10521     7360    -3161     
+ Misses        369      161     -208     
+ Partials      461      344     -117     

Flag	Coverage Δ
unittest	93.57% <100.00%> (+0.89%)	⬆️

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

Impacted Files	Coverage Δ
...n/src/rules/indent-new-do-not-use/OffsetStorage.ts	100.00% <100.00%> (ø)
...slint-plugin/src/rules/no-unnecessary-condition.ts	97.19% <100.00%> (+0.01%)	⬆️
...pe-manager/src/definition/CatchClauseDefinition.ts
packages/scope-manager/src/lib/esnext.ts
packages/scope-manager/src/lib/esnext.array.ts
packages/scope-manager/src/lib/esnext.string.ts
packages/scope-manager/src/scope/WithScope.ts
packages/scope-manager/src/lib/lib.ts
packages/scope-manager/src/lib/es2021.weakref.ts
packages/scope-manager/src/scope/BlockScope.ts
... and 168 more

[bradzacher]

thanks for this!