feat: raw strings: distinguish delimiters from actual string

We could set the delimiters to a different highlight group. Example @punctuation.special:

To see all available groups, hit :h treesitter-highlight-groups. I could see:

• @punctuation.special
• @punctuation.delimiter
• @tag.delimiter
• @string.escape
• @string.special
• @string.special.symbol

Any opinions?