editor.multicursorModifier not discoverable (add toggle menu item)

[isidorn]

Refs: #27480

The setting editor.multicursorModifier is not that discoverable, I as a user would not even think about looking there. In order to impove this I would consider adding a toggle action "Use ctrl + click to add cursor / use altr + click to add cursor" in the selection menu which already has all the multi cursor actions.

Without that the only way users find it is via googling around / stack overflow

[alexdima]

Suggestion from @seanmcbreen in #27503 (comment)

Place a toggle in the Selection menu for enabling this - I propose:
Use Ctrl Click for Multi-cursor and Use Alt Click for Multi-cursor
Make this it's own section at the bottom (less convicted on where it is just trying to propose something)

[bpasero]

Seems to work, it is not a separate section though:

[isidorn]

Yeah I believe the multicursors deserve their section and this should be the last entry in that section

[alexdima]

All those actions are about multicursor, so that's why I thought this should go with them. I am open to changing this, I don't have strong feelings either way.