Reapply "buttonbar: support dropdowns (#91886)"

[JonasBa]

Fixes the previously faulty implementation by removing the translate approach in favor of margin, and sets is so that only elements that are focused receive the z-index propagation, which omits any containers that might be holding the elements

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #91970      +/-   ##
==========================================
- Coverage   86.39%   83.97%   -2.43%     
==========================================
  Files       10356    10356              
  Lines      587429   587426       -3     
  Branches    22586    22586              
==========================================
- Hits       507531   493271   -14260     
- Misses      79471    93728   +14257     
  Partials      427      427              

[getsantry[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you remove the label Waiting for: Community, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[getsantry[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you remove the label Waiting for: Community, I will leave it alone ... forever!

---

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀