Follow-up to #27358.

Problem:  Combined highlighting was not applied to nvim_eval_statusline(),
          and 'statuscolumn' sign segment/numhl highlights.
Solution: Add an additional `groups` element to the return value of
          `nvim_eval_statusline()->highlights`. This is an array of stacked
          highlight groups (highest priority last). Also resolve combined
          highlights for the 'statuscolumn' sign segment/numhl highlights.
          Expose/synchronize some drawline.c logic that is now mimicked in
          three different places.

Problem:
The `nvim_notify` API (note: unrelated to `vim.notify()` Lua API) was
not given any real motivation in https://github.com/neovim/neovim/pull/13843

There are, and were, idiomatic and ergonomic alternatives already.

Solution:
Deprecate `nvim_notify`.

Problem:  We want to deprecate `nvim_err_write(ln)()` but there is no
          obvious replacement (from Lua). Meanwhile we already have
          `nvim_echo()` with an `opts` argument.
Solution: Add `err` argument to `nvim_echo()` that directly maps to
          `:echoerr`.

Problem:
`nvim__redraw()` doesn't clamp the lines in the `range` parameter before truncating to int. The resulting range may be empty when the original range contained buffer lines and vice versa.

E.g. for a buffer with 4 lines, these are the redrawn lines:

```lua
{ 2, 2 ^ 31 } -> none (should be { 2, 3 })
{ 2, 2 ^ 32 } -> none (should be { 2, 3 })
{ 2 ^ 32 - 1, 2 } -> { 0, 1 } (should be none)
```

Solution:
Clamp `range` values before truncating to int.

Problem:
`termopen` has long been a superficial wrapper around `jobstart`, and
has no real purpose. Also, `vim.system` and `nvim_open_term` presumably
will replace all features of `jobstart` and `termopen`, so centralizing
the logic will help with that.

Solution:
- Introduce `eval/deprecated.c`, where all deprecated eval funcs will live.
- Introduce "term" flag of `jobstart`.
- Deprecate `termopen`.

When a terminal application running inside the terminal emulator sets
the cursor shape or blink status of the cursor, update the cursor in the
parent terminal to match.

This removes the "virtual cursor" that has been in use by the terminal
emulator since the beginning. The original rationale for using the
virtual cursor was to avoid having to support additional UI methods to
change the cursor color for other (non-TUI) UIs, instead relying on the
TermCursor and TermCursorNC highlight groups.

The TermCursor highlight group is now used in the default 'guicursor'
value, which has a new entry for Terminal mode. However, the
TermCursorNC highlight group is no longer supported: since terminal
windows now use the real cursor, when the window is not focused there is
no cursor displayed in the window at all, so there is nothing to
highlight. Users can still use the StatusLineTermNC highlight group to
differentiate non-focused terminal windows.

BREAKING CHANGE: The TermCursorNC highlight group is no longer supported.

Problem:
- API functions using `try_start` directly, do not surface the
  underlying error message, and instead show generic messages.
- Error-handling code is duplicated in the API impl.
- Failure modes are not tested.

Solution:
- Use `TRY_WRAP`.
- Add tests.

Problem:
`validate_option_value_args()` returns `OK` even if option name is
invalid or if option doesn't have the supported scope, which leads to
Neovim still trying to erroneously get/set the option in those cases,
which can lead to an assertion failure when `option_has_scope()` is
invoked. This issue miraculously doesn't exist in release builds since
the assertion is skipped and `(get/set)_option_value_for` returns if
there is an error set, but that is not the intended location for that
error to be caught.

Solution:
Make `validate_option_value_args()` return `FAIL` if there is an error
set, which causes the API option functions to return early instead of
trying to get/set an invalid option.

Problem:  Documentation for "hl_group" in nvim_buf_set_extmark() is
          unclear. "hl_group" in nvim_echo() does not accept
          highlight group id.
Solution: Move documentation for highlight group name/id to first
          mention of hl_group. Update nvim_echo() to accept highlight
          group id.