length_test_linter() for length(x == 0)

[MichaelChirico]

Closes #1991.

length_equals_linter() generalized to length_test_linter() to incorporate other cases where length() is applied to a logical vector, e.g. length(x > 0).

[codecov-commenter]

Codecov Report

Merging #2124 (5d6502e) into main (02f7db8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 5d6502e differs from pull request most recent head ba6ef99. Consider uploading reports for the commit ba6ef99 to get more accurate results

@@           Coverage Diff           @@
##             main    #2124   +/-   ##
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  Coverage   99.64%   99.64%           
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  Files         111      112    +1     
  Lines        5097     5116   +19     
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+ Hits         5079     5098   +19     
  Misses         18       18           

Files Changed	Coverage Δ
R/length_test_linter.R	100.00% <100.00%> (ø)