Feature request: automatic matching pairs

Most languages have a common set of matching pairs that can be filled in by the editor automatically (e.g., ( & ), " & ") but most languages have additional matching pairs and some even have quirks.

This seems like something well suited to language servers.

Some examples:

# Ruby
# Example pair: "if" "end" on different lines
if thing_is_true
  do_something
end

" viml (AKA VimScript)
" comments are double quotes.
" but in other cases are pairs.
" another example: "function" "endfunction" on different lines
function thing(value)
  echon "string" a:value
endif

// Javascript
// example: "{" "}" on different lines (surrounding blocks)
(value) -> {
  // expect a newline here
}

# Python doesn't have many end markers
if thing
  something()

Issue 672 names no files, tests, or entry points. Start by clarifying the proposed protocol capability and how language-specific matching pairs would be represented; done would require an agreed, implementable specification.