Use standard injection.language and injection.content captures (#22268)

Closes #9656. Continuation of #9654, but with the addition of backwards
compatibility for the existing captures.

Release Notes:

- Improved Tree-sitter support with added compatibility for standard
injections captures

---------

Co-authored-by: Finn Evers <finn.evers@outlook.de>

crates/languages/src/cpp/injections.scm

@@ -1,11 +1,11 @@
 (preproc_def
-    value: (preproc_arg) @content
-    (#set! "language" "c++"))
+    value: (preproc_arg) @injection.content
+    (#set! injection.language "c++"))
 
 (preproc_function_def
-    value: (preproc_arg) @content
-    (#set! "language" "c++"))
+    value: (preproc_arg) @injection.content
+    (#set! injection.language "c++"))
 
 (raw_string_literal
-  delimiter: (raw_string_delimiter) @language
-  (raw_string_content) @content)
+  delimiter: (raw_string_delimiter) @injection.language
+  (raw_string_content) @injection.content)