vim-patch:9.2.1114: Visual selection is not highlighted at the cursor position

Problem:  In a terminal the character under the cursor is normally not
          shown as part of the visual selection.
Solution: Don't set "noinvcur" in win_line() (Shane Harper).

The problem did not occur in the GUI, only in a terminal.

The name "noinvcur" ("don't invert the cursor") was misleading: the
variable did not affect the cursor, but whether the character under the
cursor could be displayed as part of the visual selection.

The "noinvcur" handling may have been meant to help during a visual
selection when Visual is shown in reverse video and the terminal draws
the cursor by inverting the character under it, as otherwise the
character under the cursor would not look highlighted like the rest of
the selection. But Vim cannot know in general how a terminal draws the
cursor, and when either the cursor is not drawn by inverting the
character under it or Visual is not shown in reverse video, the handling
just left a character of the visual selection unhighlighted.

closes: vim/vim#21317

https://github.com/vim/vim/commit/d10aab4ba6602f8f2f2576d2d62ceb63869db6fb

Co-authored-by: Shane Harper <shane@shaneharper.net>
AI-assisted

The test uses the position col=5,row=5; but such a position
is outside of the buffer.

Presume that it was meant to be col=5,row=4...

Problem:
The magic globals `it`, `describe`, etc., are more trouble than they are
worth.

- Hooking into `after_each` requires `getfenv()` hacks.
- They confuse luals/emmylua, because the top-level `.luarc.json` isn't
  merged with `test/.luarc.json` (apparently a luals limitation?)
- They totally defeat discoverability because the user just has to
  "know" about the various magic symbols.

So they harm DX, which means they serve no purpose at all.

Solution:
- Expose the test API from `testutil`, so tests can call `t.it()`,
  `t.describe()`, etc., in the conventional way.
- Drop `getfenv()` hacks.
- Drop the `setfenv()` injection in `load_chunk`.
- Drop `test/_meta.lua`.

Co-authored-by: Yi Ming <ofseed@foxmail.com>