feat: DH-18780: Resizable column header groups

[vbabich]

• Allow dragging separators between column header groups to resize them
• Add e2e tests for hover state and drag to resize

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.16%. Comparing base (0160356) to head (53b64eb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2567      +/-   ##
==========================================
+ Coverage   44.91%   45.16%   +0.25%     
==========================================
  Files         769      769              
  Lines       43466    43463       -3     
  Branches    11173    10989     -184     
==========================================
+ Hits        19524    19632     +108     
+ Misses      23926    23815     -111     
  Partials       16       16              

Flag	Coverage Δ
unit	45.16% <100.00%> (+0.25%)	⬆️

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