fix(eslint-plugin): handle missing message IDs in eslint v5/v6

[esetnik]

Fixes #2451

[typescript-eslint]

Thanks for the PR, @esetnik!

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Thanks again!

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[codecov]

Codecov Report

Merging #2461 into master will decrease coverage by 0.11%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2461      +/-   ##
==========================================
- Coverage   92.94%   92.83%   -0.12%     
==========================================
  Files         289      289              
  Lines        9272     9283      +11     
  Branches     2583     2594      +11     
==========================================
  Hits         8618     8618              
  Misses        320      320              
- Partials      334      345      +11     

Flag	Coverage Δ
#unittest	92.83% <0.00%> (-0.12%)	⬇️

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

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/indent.ts	90.47% <0.00%> (-2.21%)	⬇️
...kages/eslint-plugin/src/rules/init-declarations.ts	76.47% <0.00%> (-4.78%)	⬇️
...ackages/eslint-plugin/src/rules/keyword-spacing.ts	92.85% <0.00%> (-7.15%)	⬇️
...nt-plugin/src/rules/lines-between-class-members.ts	85.71% <0.00%> (-6.60%)	⬇️
...ackages/eslint-plugin/src/rules/no-invalid-this.ts	95.45% <0.00%> (-4.55%)	⬇️
...ckages/eslint-plugin/src/rules/no-magic-numbers.ts	80.76% <0.00%> (-1.59%)	⬇️
...s/eslint-plugin/src/rules/no-unused-expressions.ts	88.88% <0.00%> (-5.23%)	⬇️
packages/eslint-plugin/src/rules/no-unused-vars.ts	95.38% <0.00%> (-1.50%)	⬇️
.../eslint-plugin/src/rules/no-useless-constructor.ts	95.23% <0.00%> (-4.77%)	⬇️
packages/eslint-plugin/src/rules/quotes.ts	88.88% <0.00%> (-5.23%)	⬇️
... and 1 more

[bradzacher]

Just went through and double checked all the rules. Theres a small number you can revert as they have had message ids since pre v5.

The rest are good. Thanks for doing this!

[bradzacher]

missed a few of the v4 ones - the comments are (annoyingly) hidden under the fold by github

[bradzacher]

LGTM - thanks for doing this!