Include rawstring delimiters in the tree, use for injections
In raw-strings, the delimiter can be used to indicate embedded language:
R"css( body { background: red; } )css"
This patch adds the delimiter (if present) and raw-string content as
children of the raw_string_literal.
These can be used to parse the content with an injected grammar.
Fixes https://github.com/tree-sitter/tree-sitter-cpp/issues/159
Sam McCall