Add filter expression function

[rowanseymour]

No description provided.

[codecov]

Codecov Report

Merging #1172 (16e42c4) into main (be223a6) will increase coverage by 0.00%.
The diff coverage is 92.30%.

@@           Coverage Diff           @@
##             main    #1172   +/-   ##
=======================================
  Coverage   87.77%   87.77%           
=======================================
  Files         259      259           
  Lines       10926    10946   +20     
=======================================
+ Hits         9590     9608   +18     
- Misses        919      920    +1     
- Partials      417      418    +1     

Files Changed	Coverage Δ
excellent/functions/builtin.go	97.78% <90.90%> (-0.24%)	⬇️
excellent/types/function.go	100.00% <100.00%> (ø)

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