runtime(erlang): add support for matchit plugin (vim/vim#13713)
This commit updates the Erlang runtime files to be in sync with the
`vim-erlang-runtime` repository. In particular, it adds the following
commit (with some cleanup and simplification afterwards):
6ea8b85bc918ab6c3392
Co-authored-by: Csaba Hoch <csaba.hoch@gmail.com>