feat: add internal eslint plugin for repo-specific lint rules

[bradzacher]

There's a few things I want to enforce internally.
Save us from having to communicate these things in PR reviews.

• ensuring people don't do import ts from 'typescript' in packages.
  • this breaks compat with users that don't use allowSyntheticDefaultImports
• ensuring people don't accidentally do import {} from '@typescript-eslint/typescript-estree' from the plugins, where the package isn't a dependency.
  • this breaks encapsulation, and will cause problems if we move things around in future

Adding this in now reduces the barrier to entry, meaning we can easily add rules to warn against patterns we see people do in the future.

[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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[codecov]

Codecov Report

Merging #1373 into master will decrease coverage by 0.04%.
The diff coverage is 92.42%.

@@            Coverage Diff             @@
##           master    #1373      +/-   ##
==========================================
- Coverage   94.09%   94.04%   -0.05%     
==========================================
  Files         133      139       +6     
  Lines        5940     5975      +35     
  Branches     1685     1691       +6     
==========================================
+ Hits         5589     5619      +30     
- Misses        187      192       +5     
  Partials      164      164

Impacted Files	Coverage Δ
...lint-plugin/src/rules/prefer-nullish-coalescing.ts	98.07% <ø> (ø)	⬆️
packages/eslint-plugin/src/rules/require-await.ts	100% <ø> (ø)	⬆️
packages/eslint-plugin-internal/src/index.ts	0% <0%> (ø)
packages/eslint-plugin-internal/src/rules/index.ts	0% <0%> (ø)
...ackages/eslint-plugin/src/rules/prefer-includes.ts	100% <100%> (ø)	⬆️
...estree/src/create-program/createIsolatedProgram.ts	75% <100%> (ø)	⬆️
...pt-estree/src/create-program/createWatchProgram.ts	92.3% <100%> (ø)	⬆️
...-plugin/src/rules/no-unnecessary-type-arguments.ts	92% <100%> (ø)	⬆️
packages/eslint-plugin/src/util/types.ts	82.47% <100%> (ø)	⬆️
packages/eslint-plugin-internal/src/util/index.ts	100% <100%> (ø)
... and 31 more

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