feat: bump minimum supported TS version to 4.2.4

[bradzacher]

BREAKING CHANGE:
Bumps the minimum supported range and removes handling for old versions

PR Checklist

• Addresses an existing open issue: fixes Bump minimum supported TS version to 4.2 to match DefinitelyTyped's 2y version support window #5914, fixes [no-non-null-asserted-optional-chain] Possible Infinite Loop #2521, closes fix(eslint-plugin): [no-non-null-asserted-optional-chain] infinite loop problem #5367
• That issue was marked as accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

DT hasn't bumped to 4.2 yet, but it's only just ticked to november, so I'd expect them to do it soon - likely before we do the major release.

This PR:

• updates docs to clarify our version support windows
• bumps the ranges around the place
• removes no-longer-necessary checks for now outdated versions

[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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✅ Successfully ran 46 targets

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[codecov]

Codecov Report

Merging #5915 (0c29c34) into v6 (9b5fa0b) will increase coverage by 0.25%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##               v6    #5915      +/-   ##
==========================================
+ Coverage   91.44%   91.69%   +0.25%     
==========================================
  Files         355      355              
  Lines       12058    12009      -49     
  Branches     3530     3518      -12     
==========================================
- Hits        11026    11012      -14     
+ Misses        733      701      -32     
+ Partials      299      296       -3     

Flag	Coverage Δ
unittest	91.69% <100.00%> (+0.25%)	⬆️

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

Impacted Files	Coverage Δ
packages/typescript-estree/src/version-check.ts	100.00% <ø> (ø)
...n/src/rules/no-non-null-asserted-optional-chain.ts	100.00% <100.00%> (+53.33%)	⬆️
...plugin/src/rules/no-unnecessary-type-constraint.ts	100.00% <100.00%> (+12.00%)	⬆️
packages/typescript-estree/src/convert.ts	97.85% <100.00%> (+0.25%)	⬆️
...pt-estree/src/create-program/createWatchProgram.ts	83.79% <100.00%> (+5.73%)	⬆️
...ipt-estree/src/parseSettings/warnAboutTSVersion.ts	93.33% <100.00%> (ø)

[JoshuaKGoldberg]

Is this decision documented anywhere? Now that we have more maintainer funding & people, it'd be nice to be able to support RC releases. But that's really hard and I'm guessing still not something worth it.

[bradzacher]

I'm all for us bumping versions and allowing RCs if we're able to - I just don't want us to set the expectation that we will support all RCs.

Sometimes releases are massive and and can take a lot of work to fully support.
Sometimes they have literally no impact for us.
Sometimes features from the beta get dropped from the RC.
Sometimes features from the RC get dropped from the full release.

There's just a lot of variability and with our limited bandwidth I don't want us to commit to anything!

[JoshuaKGoldberg]

#5932

[JoshuaKGoldberg]

Love to see all this code removal! Once the lints are fixed, 🚀

[JamesHenry]

Beautiful!