Helix mode search and selection improvements

[HactarCE]

Closes #41125
Closes #41164

This PR removes the out-of-band tracking of whether selection ranges should be compacted to the start of the range. That's useful for things like SelectNextMatch in vim, but it turns out not to be as universal when using vim mode as the original authors had thought, so we'd have to do silly hacks like turning that setting on and off between certain motions to get the correct behavior both for vim and helix modes.

Now you have to explicitly pass a collapse flag into the helpers having to do with buffer search selection matching, and we've migrated the relevant APIs to use that.

We also discovered a false positive in the helix tests around s used without a selection. In helix this doesn't do anything, but because of the semantics of our "search selected lines" flag, in zed it simply acts like /. We've disabled this test for now because the more faithful behavior doesn't seem necessarily more useful.

Release Notes:

• Fixed SwitchToHelixNormalMode to keep selection when hitting escape from select mode, and bound it to escape in helix select mode by default.
• Improved the behavior of vim::MoveToNextMatch and search::SelectNextMatch (as well as their previous counterparts) when using helix mode. When enabled, the latter now creates multiple selections using multicursor, unlike in vim where it simply deselects the current match and selects the next one.