Closes#26002
Release Notes:
- Added `multibuffer` key context.
- `cmd-down` and `cmd-shift-down` on Mac now moves to the end of the
last line of a singleton buffer instead of the beginning. In
multibuffers, these now move to the start of the next excerpt.
- Fixed `vim::PreviousSectionEnd` (bound to `[ ]`) to move to the
beginning of the line, matching the behavior of `vim::NextSectionEnd`.
- Added `editor::MoveToStartOfNextExcerpt` and
`editor::MoveToEndOfPreviousExcerpt`.
450d727a04