fix(core): header columns grouping misbehave after hiding column

[ghiscoding]

• some header group titles disappear after hiding a column

[codecov]

Codecov Report

Merging #164 (5587104) into master (ecfb9a7) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #164   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          200       200           
  Lines        11674     11678    +4     
  Branches      3829      3829           
=========================================
+ Hits         11674     11678    +4     

Impacted Files	Coverage Δ
...kages/common/src/extensions/headerMenuExtension.ts	100.00% <100.00%> (ø)
packages/common/src/services/grid.service.ts	100.00% <100.00%> (ø)
packages/common/src/services/gridState.service.ts	100.00% <100.00%> (ø)
.../common/src/services/groupingAndColspan.service.ts	100.00% <100.00%> (ø)
...bundle/src/components/slick-vanilla-grid-bundle.ts	100.00% <100.00%> (ø)

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