Check against this usage in computed functions

[emilos]

I was going through the source code to learn how it works and I noticed a TODO for missing validation in the computed functions section, I even tried to use this there some time ago. Hopefully this helps a little :)

[codecov-io]

Codecov Report

Merging #1033 into master will increase coverage by 0.01%.
The diff coverage is 77.27%.

@@            Coverage Diff             @@
##           master    #1033      +/-   ##
==========================================
+ Coverage   91.99%   92.01%   +0.01%     
==========================================
  Files         119      121       +2     
  Lines        4361     4368       +7     
  Branches     1406     1408       +2     
==========================================
+ Hits         4012     4019       +7     
  Misses        148      148              
  Partials      201      201

Impacted Files	Coverage Δ
src/validate/js/propValidators/helpers.ts	100% <100%> (+21.73%)	⬆️
src/validate/js/propValidators/computed.ts	100% <100%> (ø)	⬆️
src/utils/isThisGetCallExpression.ts	100% <100%> (ø)
src/utils/walkThroughTopFunctionScope.ts	37.5% <37.5%> (ø)

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[Rich-Harris]

Thank you!