fix multicursor snippet placeholder directions

[pascalkuthe]

Closes #8422

The code worked as intended for the most part, the head < anchor and anchor < head case was just swapped accidentally. This caused a selection to be created from the first tabstop to the anchor (if the selection is forward) which would be merged with all other tabstop selections.

[perlinm]

Confirming that I tested this locally and it fixes #8422! Thank you!

Minor addendum: with these changes, whether I move the cursor after entering insert-mode no longer affects the cursor location(s), but it still affects what text is selected when I add the snippet. Any ideas why that might be and how to fix it? Not a huge deal if this isn't resolved 🙂

[pascalkuthe]

that is on purpose, we only move the selection head and not the anchor. for example if you use |\be| selected and then enter insert mode with a and select the completion you should endup with

|\begin{|}

\end{||}

This matches what would happen if you manually type same if the cursor is in the reverse direction in insertmode.

Movement does change the cursor direction (to forward) outside of select mode