fix(formatters): date US Formatters should accept ISO date input

[ghiscoding]

• also make all Formatter arguments never undefined

[codecov]

Codecov Report

Merging #640 (482d0f5) into master (13809b4) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #640   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          154       154           
  Lines        10301     10304    +3     
  Branches      3614      3617    +3     
=========================================
+ Hits         10301     10304    +3     

Impacted Files	Coverage Δ
...-slickgrid/formatters/collectionEditorFormatter.ts	100.00% <100.00%> (ø)
...ngular-slickgrid/formatters/collectionFormatter.ts	100.00% <100.00%> (ø)
...angular-slickgrid/formatters/formatterUtilities.ts	100.00% <100.00%> (ø)

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