Put cursor at _start_ of blank pattern when removing elements, not end

[StachuDotNet]

Given the Dark code let x = (___,|2,3), hitting backspace changes it to let x = (|___,3), with the cursor at the start of the blank.

The equivalent, for the tuple match pattern, was different. It turned:

match (1,2)
  (___,|2,3) -> ___

into

match (1,2)
  (|___,3) -> ___

This was done by updating caretTargetForEndOfPattern to offset the cursor position by 0 rather than by 3.
There was a relevant note in place, and this seemed an appropriate time to follow the note.

[pbiggar]

Yeah, seems nicer