Ref T12616. Fixes T12153. Currently, when you hide inlines, they hide completely and turn into a little bubble on the previous line.
Instead, collapse them to a single line one-by-one. Narrowly, this fixes T12153.
In the future, I plan to make these changes so this feature makes more sense:
- Introduce global "hide everything" states (T8909) so you can completely hide stuff if you want, and this represents more of a halfway state between "nuke it" and "view it".
- Make the actual rendering better, so it says "epriestley: blah blah..." instead of just "..." -- and looks less dumb.
The real goal here is to introduce DiffInline and continue moving stuff from the tangled jungle of a million top-level behaviors to sensible smooth statefulness.
