GRMLBASE/90-update-alternatives: support vim >=2:8.1.2136-1

GRMLBASE/90-update-alternatives: support vim >=2:8.1.2136-1

vim 2:8.1.2136-1 moved /usr/bin/vim.* into /usr/libexec/vim/,
so we need to check for its base path.

Also vim-gtk became a transitional package for vim-gtk3 and
the binary is called vim.gtk3, add according additional check.

Fixes:

| Setting vim.gtk as editor using update-alternatives.
| update-alternatives: error: alternative /usr/bin/vim.gtk for editor not registered; not setting
| GRMLBASE/90-update-alternatives FAILED with exit code 2.