The new version of the lua client uses libmpack as a backend, and some test
scripts had to be updated to reflect that.

Luv is a simple lua binding to libuv, which is now used by neovim lua client.
The bundled luv installation a bit different from other dependencies in that it
is installed two times:

- The "BuildLuv.cmake" script downloads and installs a static version of luv
  using its normal cmake build script. This static version will be used later.
- Luv default rockspec is replaced with the alternate under the "rockspecs"
  directory(the alternate rockspec plays nicer with neovim build system)
- The alternate rockspec is used to build/install the lua module and make it
  available to lua scripts.

Also add a functionaltest-lua target to run the functional tests using the lua
interpreter and corresponding helper to top-level Makefile

New feature: `VTermState->mode.bracketpaste`
  Enabled by default, but note that `vterm_state_reset()` disables it.
  https://github.com/neovim/libvterm/commit/03981def6baedf459ff1539531f8a389520038fa
References #3476

New feature: `vterm_state_set_unrecognised_fallbacks`
  https://github.com/neovim/libvterm/commit/acf7f19713587df91ab9bb26c84a2c9a22ba8745

Oh, and terminal reflow works now.
Closes #2514 (but not #3864, that's a bit more tricky)

Although UNIX is a registered trademark of The Open Group, it doesn't
really matter whether we refer to these systems as UNIX, Unix, or
Unix-like. So, for consistency, refer to them collectively as Unix.

Related:
http://www.greens.org/about/unix.html
http://www.unixica.com/html/unixunix.html

Otherwise the dynamic library is built also and find_library will prefer
that over the static one. That results in linking against the dynamic
library which will not be found after install.

This code:
  https://github.com/neovim/neovim/blob/8b3c399b6d7f4a277d80da4b29349fed944f7d46/third-party/CMakeLists.txt#L130
should prevent the above problem, but it doesn't hurt to be explicit.