injections(cpp): add injections for raw string literals

the delimiter describes the language to use for the injection content

```cpp
auto python_code = R"python(
  import os

  if __name__ == '__main__':
    print(os.name)
)python";
```

queries/cpp/injections.scm

@@ -1,3 +1,7 @@
 (preproc_arg) @cpp
 
 (comment) @comment
+
+(raw_string_literal
+  delimiter: (raw_string_delimiter) @language
+  (raw_string_content) @content)