Truncate too long focused group names

[acelaya]

Part of hypothesis/product-backlog#1660
Depends on #7292

Since the horizontal space available in the sidebar is limited, this PR ensures the name of the focused group is truncated with an ellipsis if it cannot fit the space left by the toolbar.

The entire group name can still be seen when hovering over it.

With a long group name, this is how it was seen before these changes:

And after:

Considerations

This is just part of a solution to multiple problems. The next pieces of work are described in hypothesis/product-backlog#1660 (comment), and will come after.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.47%. Comparing base (e1ee0df) to head (1aa7e18).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7289   +/-   ##
=======================================
  Coverage   99.47%   99.47%           
=======================================
  Files         271      271           
  Lines       10947    10948    +1     
  Branches     2618     2618           
=======================================
+ Hits        10889    10890    +1     
  Misses         58       58           

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