cpp: Add injection for raw string literals (#13726)

Release Notes:

- N/A

Before: 

![Screenshot_20240701_231801](https://github.com/zed-industries/zed/assets/66138117/d0df7819-09e7-4a3b-949d-78e04ff63b23)

After:

![Screenshot_20240702_162856](https://github.com/zed-industries/zed/assets/66138117/943136e1-3b15-482e-bf45-2571cd212eaf)

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/languages/src/cpp/highlights.scm

@@ -137,6 +137,7 @@
   ":"
   "::"
   ";"
+  (raw_string_delimiter)
 ] @punctuation.delimiter
 
 [

crates/languages/src/cpp/injections.scm

@@ -5,3 +5,7 @@
 (preproc_function_def
     value: (preproc_arg) @content
     (#set! "language" "c++"))
+
+(raw_string_literal
+  delimiter: (raw_string_delimiter) @language
+  (raw_string_content) @content)