Now `:InspectTree` will show missing nodes as e.g. `(MISSING identifier)`
or `(MISSING ";")` rather than just `(identifier)` or `";"`. This is
doable because the `MISSING` keyword is now valid query syntax.

Co-authored-by: Christian Clason <c.clason@uni-graz.at>

Before #31525 the prompts had a trailing space.
Also add a test for #7857.

Follow-up to #27358.

They are no longer necessary after #31562, as busy_start and busy_stop
are no longer emitted by terminal buffers with visible cursor.

Problem:  getchar_spec may fail when screen:expect_unchanged() doesn't
          wait long enough.
Solution: Add poke_eventloop() before screen:expect_unchanged().

Problem:  'diffopt' "linematch" cannot be used with {n} less than 10
          digits (after v9.1.1022)
Solution: Fix off-by-one error when checking for digit (zeertzjq)

closes: vim/vim#16577

https://github.com/vim/vim/commit/ccd7f454fcac2f99085d4f50e79c111c02741166

Problem:  no sanitize check when running linematch
Solution: add sanitize check before applying the linematch algorithm,
          similar to diff_find_change() (Jonathon)

closes: vim/vim#16446

https://github.com/vim/vim/commit/ca307efe486670b76563a4a287bc94dace57fb74

Co-authored-by: Jonathon <jonathonwhite@protonmail.com>

Problem:  linematch option value not completed
          (after v9.1.1009)
Solution: Update diffoption completion values

related: vim/vim#9661
closes: vim/vim#16437

https://github.com/vim/vim/commit/9162e636b31dcac57876cbdec15a683cedd9760e

Co-authored-by: Christian Brabandt <cb@256bit.org>

Problem:  diff feature can be improved
Solution: include the linematch diff alignment algorithm
          (Jonathon)

closes: vim/vim#9661

https://github.com/vim/vim/commit/7c7a4e6d1ad50d5b25b42aa2d5a33a8d04a4cc8a

Co-authored-by: Jonathon <jonathonwhite@protonmail.com>