Before this change, "static inline" functions in headers needed to have
their function attributes specified in a completely different way. The
prototype had to be duplicated, and REAL_FATTR_ had to be used instead
of the public FUNC_ATTR_ names.

TODO: need a check that a "header.h.inline.generated.h" file is not
forgotten when the first "static inline" function with attributes
is added to a header (they would just be silently missing).

Remove `export` pramgas from defs headers as it causes IWYU to believe
that the definitions from the defs headers comes from main header, which
is not what we really want.

FUNC_ATTR_* should only be used in .c files with generated headers.
Defining FUNC_ATTR_* as empty in headers causes misuses of them to be
silently ignored. Instead don't define them by default, and only define
them as empty after a .c file has included its generated header.

It is less error-prone than manually defining header guards. Pretty much
all compilers support it even if it's not part of the C standard.

Fix remaining clint errors and remove error suppression completely.

Rename the lint targets to align with the established naming convention:

- lintc-clint lints with clint.py.
- lintc-uncrustify lints with uncrustify.
- lintc runs both targets.

lintc is also provided as a make target for convenience.

After this change we can remove these files:
https://github.com/neovim/doc/tree/gh-pages/reports/clint
https://github.com/neovim/doc/blob/main/ci/clint-errors.sh

It's confusing to mix vendored dependencies with neovim source code. A
clean separation is simpler to keep track of and simpler to document.

Note for external UIs: Nvim can now emit multiple "redraw" event batches
before a final "flush" event is received. To retain existing behavior,
clients should make sure to update visible state at an explicit "flush"
event, not just the end of a "redraw" batch of event.

* Get rid of copy_object() blizzard in the auto-generated ui_event layer
* Special case "grid_line" by encoding screen state directly to
  msgpack events with no intermediate API events.
* Get rid of the arcane notion of referring to the screen as the "shell"
* Array and Dictionary are kvec_t:s, so define them as such.
* Allow kvec_t:s, such as Arrays and Dictionaries, to be allocated with
  a predetermined size within an arena.
* Eliminate redundant capacity checking when filling such kvec_t:s
  with values.