feat(eslint-plugin): add rule restrict-template-expressions

[phaux]

Closes #818

(I'm submitting these PRs via VSCode extension and that's why I have to edit the title afterwards)

[typescript-eslint]

Thanks for the PR, @phaux!

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[glen-84]

Would it be possible to allow any, for codebases that are not yet fully typed?

[ckknight]

Instead of options like allowBoolean or allowNumber, why not allow configuration like allowed: ['number', 'bigint', 'boolean', 'null']?

[phaux]

@glen-84 Noted.

@ckknight I was actually considering going into the other direction: allow "loose" option which enables all types which have obvious string representation, but later I split that into 3 separate options. Having 5 options is too much IMO. Also, I can't think of a case where you would want only one of number | bigint or null | undefined

[ark120202]

@phaux I'm not sure how common it would be, but one advantage of using a more generic filter would be an ability to allow some application-specific types with expected toString implementation.

[bradzacher]

LGTM - thanks for this!

[codecov]

Codecov Report

Merging #850 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #850      +/-   ##
==========================================
+ Coverage   94.17%   94.22%   +0.05%     
==========================================
  Files         124      125       +1     
  Lines        5322     5371      +49     
  Branches     1492     1509      +17     
==========================================
+ Hits         5012     5061      +49     
  Misses        177      177              
  Partials      133      133

Impacted Files	Coverage Δ
...-plugin/src/rules/restrict-template-expressions.ts	100% <100%> (ø)
packages/eslint-plugin/src/rules/index.ts	100% <100%> (ø)	⬆️