feat: add rowspan implementation

[ghiscoding]

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 20.91%. Comparing base (e3f4892) to head (68dfb1e).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...slickgrid/src/custom-elements/aurelia-slickgrid.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1307   +/-   ##
=======================================
  Coverage   20.91%   20.91%           
=======================================
  Files           8        8           
  Lines         952      952           
  Branches      327      327           
=======================================
  Hits          199      199           
  Misses        753      753           

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