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>

extensions/php/languages/php/injections.scm

@@ -1,9 +1,9 @@
-((text) @content
- (#set! "language" "html")
- (#set! "combined"))
+((text) @injection.content
+ (#set! injection.language "html")
+ (#set! injection.combined))
 
-((comment) @content
-  (#match? @content "^/\\*\\*[^*]")
-  (#set! "language" "phpdoc"))
+((comment) @injection.content
+  (#match? @injection.content "^/\\*\\*[^*]")
+  (#set! injection.language "phpdoc"))
 
-((heredoc_body) (heredoc_end) @language) @content
+((heredoc_body) (heredoc_end) @injection.language) @injection.content