feat: bump minimum required TS version

[bradzacher]

BREAKING CHANGE:

closes #1774
closes #1759

[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 #2004 into v3 will increase coverage by 0.11%.
The diff coverage is 88.18%.

@@            Coverage Diff             @@
##               v3    #2004      +/-   ##
==========================================
+ Coverage   93.64%   93.75%   +0.11%     
==========================================
  Files         169      176       +7     
  Lines        7677     7814     +137     
  Branches     2193     2240      +47     
==========================================
+ Hits         7189     7326     +137     
+ Misses        229      228       -1     
- Partials      259      260       +1     

Flag	Coverage Δ
#unittest	93.75% <88.18%> (+0.11%)	⬆️

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/ban-ts-comment.ts	100.00% <ø> (ø)
packages/eslint-plugin/src/rules/ban-ts-ignore.ts	100.00% <ø> (ø)
packages/eslint-plugin/src/rules/camelcase.ts	92.85% <ø> (ø)
...kages/eslint-plugin/src/rules/class-name-casing.ts	100.00% <ø> (ø)
...int-plugin/src/rules/consistent-type-assertions.ts	86.48% <ø> (ø)
...-plugin/src/rules/explicit-function-return-type.ts	100.00% <ø> (ø)
...plugin/src/rules/explicit-module-boundary-types.ts	82.60% <ø> (ø)
...s/eslint-plugin/src/rules/interface-name-prefix.ts	100.00% <ø> (ø)
.../eslint-plugin/src/rules/member-delimiter-style.ts	94.44% <ø> (ø)
...kages/eslint-plugin/src/rules/naming-convention.ts	88.51% <ø> (ø)
... and 69 more