feat(experimental-utils): add suggestion property for rule modules

[G-Rath]

This property doesn't seem to be used for anything by ESLint (suggestions still work without it), but it's in the docs, and would let us plugin devs check if our rules have suggestions for documentation generation tooling.

[typescript-eslint]

Thanks for the PR, @G-Rath!

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 #2033 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2033   +/-   ##
=======================================
  Coverage   93.93%   93.93%           
=======================================
  Files         172      172           
  Lines        7829     7829           
  Branches     2245     2245           
=======================================
  Hits         7354     7354           
  Misses        217      217           
  Partials      258      258           

Flag	Coverage Δ
#unittest	93.93% <ø> (ø)

Impacted Files	Coverage Δ
...gin-internal/src/rules/no-poorly-typed-ts-props.ts	88.88% <ø> (ø)
...ages/eslint-plugin/src/rules/no-empty-interface.ts	96.15% <ø> (ø)
...ackages/eslint-plugin/src/rules/no-explicit-any.ts	92.85% <ø> (ø)
...es/eslint-plugin/src/rules/no-floating-promises.ts	100.00% <ø> (ø)
...n/src/rules/no-non-null-asserted-optional-chain.ts	100.00% <ø> (ø)
...s/eslint-plugin/src/rules/no-non-null-assertion.ts	84.37% <ø> (ø)
...ackages/eslint-plugin/src/rules/prefer-as-const.ts	100.00% <ø> (ø)
...lint-plugin/src/rules/prefer-nullish-coalescing.ts	98.07% <ø> (ø)
...s/eslint-plugin/src/rules/prefer-optional-chain.ts	95.23% <ø> (ø)
...nt-plugin/src/rules/switch-exhaustiveness-check.ts	97.67% <ø> (ø)

[bradzacher]

thanks!