build: various build improvements

- 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.

CMakeLists.txt

@@ -228,7 +228,7 @@ endif()
 find_program(SHELLCHECK_PRG shellcheck ${LINT_REQUIRED})
 find_program(STYLUA_PRG stylua ${LINT_REQUIRED})
 
-set(STYLUA_DIRS runtime scripts src test)
+set(STYLUA_DIRS runtime scripts src test contrib)
 
 add_glob_target(
   TARGET lintlua-luacheck