vim: Fix indentation of 'closing parens only lines'

This commit changes the indentation of lines which contain only closing parentheses ()).

Example:

Change

add_library(mylib
    mysrc.c
    )

to:

add_library(mylib
    mysrc.c
)

There are edge cases, where the indentation still doesn't really work.

Example:

This, admittedly weird, piece of code (manually formatted to what I would expect - this is already a personal preference ...):

  if(4)
      if((0 OR 1
         )
        ) # could also be aligned with the `i` in `if`
          set(foobar
          )
      endif()
      set(foobar)
  endif()

will be changed to:

  if(4)
      if((0 OR 1
  )
      )
      set(foobar
      )
  endif()
  set(foobar)
  endif()

whereas with the previous vim indentation code the result would have been:

  if(4)
      if((0 OR 1
          )
      )
  set(foobar
      )
      endif()
      set(foobar)
  endif()

which is not great but better than above. I hope that this is acceptable.

Note: Apart from the actual indentation fixes, I based the change on a version of indent/cmake.vim I found in the debian/bookworm vim82 package which is newer than the one in the cmake repository (with Last Change: 2017 Sep 24 comment instead of the cmake repo version with Last Change: 2017 Aug 30).

This vim82/debian version moved these two lines:

let s:keepcpo= &cpo
set cpo&vim

a bit further down (after an early exit check - which seems to make sense to me).

Fixes: #22394 (closed)