Extract Scheme and Racket language support into extensions (#10442)

Release Notes:

- Extracted Scheme and Racket language support into extensions.

---------

Co-authored-by: Marshall <marshall@zed.dev>

extensions/racket/languages/racket/brackets.scm

@@ -0,0 +1,3 @@
+("(" @open ")" @close)
+("[" @open "]" @close)
+("{" @open "}" @close)

extensions/racket/languages/racket/config.toml

@@ -0,0 +1,10 @@
+name = "Racket"
+grammar = "racket"
+path_suffixes = ["rkt"]
+line_comments = ["; "]
+autoclose_before = "])"
+brackets = [
+    { start = "[", end = "]", close = true, newline = false },
+    { start = "(", end = ")", close = true, newline = false },
+    { start = "\"", end = "\"", close = true, newline = false },
+]

extensions/racket/languages/racket/indents.scm

@@ -0,0 +1,3 @@
+(_ "[" "]") @indent
+(_ "{" "}") @indent
+(_ "(" ")") @indent

extensions/racket/languages/racket/outline.scm

@@ -0,0 +1,10 @@
+(list
+    .
+    (symbol) @start-symbol @context
+    .
+    [
+        (symbol) @name
+        (list . (symbol) @name)
+    ]
+    (#match? @start-symbol "^define")
+) @item