add support for xml language

[mazunki]

I was undecided between function and class for tags here. Ideally they should just be called @tag I feel like, but alas, this is what HTML uses, which is why I went with that.

Related to nvim-mini/mini.nvim#2417

[kiyoon]

• attribute.inner includes the quotes. cit on id="1" leaves id= and you retype the quotes. This repo's HTML query excludes them and produces no capture for an empty value, jsx does the same.
• comment.inner equals comment.outer. Most languages here trim the delimiters, HTML defines no inner at all. Use #offset! 0 4 0 -3, with a guard for the empty <!----> comment, where the zero-width range misbehaves
• The _+ @function.inner pattern and the (EmptyElemTag) @function.outer pattern are redundant. tree-sitter-xml wraps all children in one content node, so both duplicate the pattern above them.