chore: start a style guide

[dyladan]

This should be considered a living document. Please make suggestions for additional rules if you feel there is something important that has been missed.

[codecov]

Codecov Report

Merging #2683 (a29c633) into main (d9e12e2) will not change coverage.
The diff coverage is n/a.

❗ Current head a29c633 differs from pull request most recent head e69256c. Consider uploading reports for the commit e69256c to get more accurate results

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  Coverage   92.52%   92.52%           
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  Files         144      144           
  Lines        5177     5177           
  Branches     1102     1102           
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  Hits         4790     4790           
  Misses        387      387           

[legendecas]

👍

[vmarchaud]

i believe we should advise against using null and prefer using undefined (even though we treat them as the same) too

[dyladan]

i believe we should advise against using null and prefer using undefined (even though we treat them as the same) too

e69256c (#2683)