feat: Cherry-pick DH-18780: Resizable column header groups (#2567)

[vbabich]

Cherry-pick #2567 into v0.85

• 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 48.43%. Comparing base (09658d1) to head (b4d63e3).

Additional details and impacted files

@@                Coverage Diff                @@
##           release/v0.85    #2575      +/-   ##
=================================================
- Coverage          48.43%   48.43%   -0.01%     
=================================================
  Files                712      712              
  Lines              39737    39734       -3     
  Branches            9924    10111     +187     
=================================================
- Hits               19247    19244       -3     
  Misses             20477    20477              
  Partials              13       13              

Flag	Coverage Δ
unit	48.43% <100.00%> (-0.01%)	⬇️

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