feat(perf): improve date sorting speed

[ghiscoding]

Here's a quick perf date sorting test before & after code change with 50k rows and 8 columns
note: the date are all in ISO format (yyyy-mm-dd), it might be even bigger differences with non-ISO format

BEFORE

1st pass

sorting ASC: 2255.841064453125 ms
sorting DESC: 676.7099609375 ms
sorting ASC: 644.962646484375 ms
sorting DESC: 671.908935546875 ms

2nd pass

sorting ASC: 1981.27978515625 ms
sorting DESC: 692.999755859375 ms
sorting ASC: 673.643798828125 ms
sorting DESC: 670.118896484375 ms

AFTER

1st pass

sorting ASC: 1059.22802734375 ms
sorting DESC: 126.10400390625 ms
sorting ASC: 336.77685546875 ms
sorting DESC: 143.007080078125 ms

2nd pass

sorting ASC: 903.991943359375 ms
sorting DESC: 143.51708984375 ms
sorting ASC: 374.537109375 ms
sorting DESC: 117.73583984375 ms

[codecov]

Codecov Report

Merging #691 (22bbe44) into master (1b89e2f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #691   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          157       157           
  Lines        10474     10474           
  Branches      3681      3681           
=========================================
  Hits         10474     10474           

Impacted Files	Coverage Δ
...modules/angular-slickgrid/sorters/dateUtilities.ts	100.00% <100.00%> (ø)

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