ocaml: Add Dune language support (#17886)

This uses my fork of the dune tree-sitter grammar to include the
generated files

Release Notes:

- N/A

extensions/ocaml/languages/dune/config.toml

@@ -0,0 +1,8 @@
+name = "Dune"
+grammar = "dune"
+path_suffixes = ["dune", "dune-project"]
+brackets = [
+  { start = "(", end = ")", close = true, newline = true },
+  { start = "\"", end = "\"", close = true, newline = false, not_in = ["string"] }
+]
+tab_size = 2

extensions/ocaml/languages/dune/highlights.scm

@@ -0,0 +1,5 @@
+(stanza_name) @function
+(field_name) @property
+(quoted_string) @string
+(multiline_string) @string
+(action_name) @keyword

extensions/ocaml/languages/dune/injections.scm

@@ -0,0 +1,2 @@
+((ocaml_syntax) @injection.content
+ (#set! injection.language "ocaml"))