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/elixir/languages/elixir/injections.scm

@@ -2,6 +2,6 @@
 
 ((sigil
   (sigil_name) @_sigil_name
-  (quoted_content) @content)
+  (quoted_content) @injection.content)
  (#eq? @_sigil_name "H")
- (#set! language "heex"))
+ (#set! injection.language "heex"))

extensions/elixir/languages/heex/injections.scm

@@ -4,10 +4,10 @@
       (partial_expression_value)
       (expression_value)
       (ending_expression_value)
-    ] @content)
-  (#set! language "elixir")
-  (#set! combined)
+    ] @injection.content)
+  (#set! injection.language "elixir")
+  (#set! injection.combined)
 )
 
-((expression (expression_value) @content)
- (#set! language "elixir"))
+((expression (expression_value) @injection.content)
+ (#set! injection.language "elixir"))