Since regex is almost always injected into other languages,
`pattern_character`s will inherit the highlight for the structure that
injects them (for example `/foo/` in JavaScript or `~r/foo/` in Elixir).
This removes the string highlight when used in the prompt.
We also add `ERROR` node highlighting so that errors in regex syntax
appear in the prompt. This resolves a TODO in the `regex_prompt`
function about highlighting errors in the regex.
* add tree-sitter-regex
* adapt regex highlights from upstream
* inject regex into elixir sigil_r/2 and sigil_R/2
* generate lang-support docs
* capture interesting nodes in character-ranges
* make $.character_class captures more consistent
* fix fallthrough behavior for character classes
* capture pattern characters as 'string'
* use latest tree-sitter-regex
* set elixir regex injections as combined
* add link to upstream queries
* inject regex in rust into 'Regex::new' raw string literals
