workspace: Add setting to make dock resize apply to all panels

[Aaron-212]

Re: #19015 Close #12667

When dragging a dock’s resize handle, only the active panel grows or shrinks. This patch introduces an opt-in behaviour that lets users resize every panel hosted by that dock at once.

Release Notes:

• Added new resize_all_panels_in_dock setting to optionally resize every panel in a dock together.

[mikayla-maki]

I'm wondering if this should actually be a default? The existing behavior seems surprising.

[Aaron-212]

IMO it should be. Clicking through left panels with different width makes the buffer editor jumps left and right.

[ConradIrwin]

See also #30946 which takes a different approach to the same issue.

[mikayla-maki]

Thank you!