csharp: Add brackets.scm (#22936)

This pull request adds the missing `brackets.scm` for the C#-extension.

Release Notes:

- N/A

extensions/csharp/languages/csharp/brackets.scm

@@ -0,0 +1,5 @@
+("(" @open ")" @close)
+("[" @open "]" @close)
+("{" @open "}" @close)
+("<" @open ">" @close)
+("\"" @open "\"" @close)