Add KtMap.filterKeys and KtMap.filterValues

[passsy]

Add KtMap.filterKeys and KtMap.filterValues

[codecov]

Codecov Report

Merging #84 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #84      +/-   ##
==========================================
+ Coverage   99.71%   99.71%   +<.01%     
==========================================
  Files          40       40              
  Lines        1758     1774      +16     
==========================================
+ Hits         1753     1769      +16     
  Misses          5        5

Impacted Files	Coverage Δ
lib/src/collection/kt_map.dart	100% <ø> (ø)	⬆️
...src/collection/extension/map_extensions_mixin.dart	100% <100%> (ø)	⬆️

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