Closes #40360

This PR added heuristics to determine what variable/breakpoint list
entry has the longest width when rendered. I added this in so the
uniform list would correctly determine which item has the longest width
and use that to calculate the scrollbar size.

The heuristic can be off if a non-mono space font is used in the UI; in
most cases, it's more than accurate enough though.

Release Notes:

- debugger: Add horizontal scroll bars to variable list, memory view,
and breakpoint list

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Co-authored-by: MrSubidubi <dev@bahn.sh>