Problem:
Subdirectories like "visual", "insert", "normal" encourage people to
separate *related* tests for no good reason.  Typically the _mode_ is
not the relevant topic of a test (and when it is, _then_ create
an appropriate describe() or it()).

Solution:
- Delete the various `test/functional/<mode>/` subdirectories, move
  their tests to more meaningful topics.
- Rename `…/normal/` to `…/editor/`.
  - Move or merge `…/visual/*` and `…/insert/*` tests into here where
    appropriate.
- Rename `…/eval/` to `…/vimscript/`.
  - Move `…/viml/*` into here also.

* test(reorg): insert/* => editor/mode_insert_spec.lua
* test(reorg): cmdline/* => editor/mode_cmdline_spec.lua
* test(reorg): eval core tests => eval_spec.lua

The commit summary maybe does not make sense, but calling a function
that does not wait on anything `wait()` makes even less sense.

Problem:    Extending sign and foldcolumn below the text is confusing.
Solution:   Let the sign and foldcolumn stop at the last text line, just like
            the line number column.  Also stop the command line window leader.
            (Christian Brabandt)

https://github.com/vim/vim/commit/8ee4c01b8c79a29065c1af05e5d9c0721069765f

Closes https://github.com/neovim/neovim/issues/9613

Update src/nvim/auevents.lua

Co-Authored-By: chemzqm <chemzqm@gmail.com>

closes #8345