new methods firstNotNullOf and firstNotNullOfOrNull for KtList

[hugobrancowb]

Closes #162

firstNotNullOf and firstNotNullOfOrNull doc reference

[passsy]

Kotlin impl

[codecov]

Codecov Report

Merging #188 (8535411) into master (64323fc) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 8535411 differs from pull request most recent head 612cb62. Consider uploading reports for the commit 612cb62 to get more accurate results

@@           Coverage Diff           @@
##           master     #188   +/-   ##
=======================================
  Coverage   99.21%   99.22%           
=======================================
  Files          40       40           
  Lines        1919     1926    +7     
=======================================
+ Hits         1904     1911    +7     
  Misses         15       15           

Flag	Coverage Δ
unittests	99.22% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
lib/src/collection/kt_list.dart	97.86% <100.00%> (+0.08%)	⬆️

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[passsy]

Awesome, thanks for your contribution!