Debugging dependencies is rare so a Debug build type is usually not
needed. In cases where it _is_ needed it is easy to rebuild in Debug
mode. But since Release builds are more common, it makes more sense as a
default.

For Neovim itself we stick with a Debug build as a default, since
rebuilding and debugging is done _much_ more frequently than with
dependencies (which we _mostly_ expect to "just work").

Also remove the CMAKE_BUILD_TYPE variable in the Makefile, since this is
set by default in CMake.

- remove "ran-" prefix from touch files as it's redundant since the
  they're already in the directory named `touches`.
- Include `contrib` when formatting with `make formatlua`.
- Use TARGET_FILE generator expression instead of assuming the
  executable location.
- reuse logic that determines whether to use lua or luajit.
- add translations to the `nvim` target.

Makefile improvements:
- rename variable `CMAKE_PRG` to `CMAKE` to make it more consistent with
  the builtin `MAKE` variable.
- stop propagating flags to generator. Users should use cmake for
  non-standard use cases.
- remove `+` prefix from targets. If the user for whatever reason wants
  to dry-run a target then they should be able to.

separate_arguments() doesn't operate in place on a variable.  It expects
a string argument to parse and stores the results in the specified
variable.

- add EXTERNALPROJECT_OPTIONS variable to main build
- use `REQUIRED` keyword for IWYU.
- remove check_c_compiler_flag checks when `ENABLE_COMPILER_SUGGESTIONS`
  is `ON`. If we explicitly enable it then we probably want it to give
  an error if it doesn't exist, rather than silently skip it.
- Move dependency interface libraries to their find module and use them
  as a pseudo-imported target.
- Remove BUSTED_OUTPUT_TYPE. It's not used and we can reintroduce it
  again if something similar is needed.
- Use LINK_OPTIONS intead of LINK_FLAGS when generating the `--version`
  output.

The benefits are primarily being able to use FetchContent, which allows
for a more flexible dependency handling. Other various quality-of-life
features such as `-B` and `-S` flags are also included.

This also removes broken `--version` generation as it does not work for
version 3.10 and 3.11 due to the `JOIN` generator expression.

Reference: https://github.com/neovim/neovim/issues/24004

Having two separate find_package calls makes it harder to maintain.

This will ensure that we can pass flags and make adjustments from the
top level cmake file instead of digging through the cmake directory.
More importantly, this will only format files that have been changed.
This has a slightly higher initial cost compared to previous solution as
all files must be initially formatted, but the gained speed up should
more than make up for it quickly.

`make formatlua` is always run due to a quirk of stylua of always changing
modification time of the file regardless if there were any changes. This is not
a major blocker as stylua is very fast.

This is a proof of concept/WIP to evaluate the viability of vendoring
libtermkey as it's been deprecated.