fix(pinning): reordering cols position freezing cols shouldn't affect

[ghiscoding]

• the steps to reproduce the issue was to create a grid with frozenColumn in the grid options, then change column position (cols reordering) and finally open header menu and freeze any of the column and the bug was that it was going back to original positions while it should keep new positions and just add new freeze column

[codecov]

Codecov Report

Merging #708 (235c664) into master (2d686ff) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #708   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          159       159           
  Lines        10615     10624    +9     
  Branches      3755      3755           
=========================================
+ Hits         10615     10624    +9     

Impacted Files	Coverage Δ
...lickgrid/components/angular-slickgrid.component.ts	100.00% <100.00%> (ø)
...ngular-slickgrid/extensions/headerMenuExtension.ts	100.00% <100.00%> (ø)
...r-slickgrid/services/groupingAndColspan.service.ts	100.00% <100.00%> (ø)
...dules/angular-slickgrid/services/shared.service.ts	100.00% <100.00%> (ø)

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