refactor: use set for reserved words

[dnalborczyk]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

[codecov]

Codecov Report

Merging #4298 (0aaa271) into master (49d41f7) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4298   +/-   ##
=======================================
  Coverage   98.45%   98.45%           
=======================================
  Files         205      205           
  Lines        7311     7311           
  Branches     2082     2082           
=======================================
  Hits         7198     7198           
  Misses         55       55           
  Partials       58       58           

Impacted Files	Coverage Δ
src/utils/exportNames.ts	100.00% <100.00%> (ø)
src/utils/generateCodeSnippets.ts	97.29% <100.00%> (ø)
src/utils/reservedNames.ts	100.00% <100.00%> (ø)
src/utils/safeName.ts	100.00% <100.00%> (ø)

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[lukastaegert]

I am sure this will be slightly slower from a performance perspective (because object access is incredibly fast, especially if the object is never mutated and initialized with a literal) but I guess it will not be noticeable.