Extract Protocol Buffers support into an extension (#18704)

This PR extracts the Protocol Buffers support into an extension.

Release Notes:

- Removed built-in support for Protocol Buffers, in favor of making it
available as an extension. The Protocol Buffers extension will be
suggested for download when you open a `.proto` file.

extensions/proto/extension.toml

@@ -0,0 +1,11 @@
+id = "proto"
+name = "Proto"
+description = "Protocol Buffers support."
+version = "0.1.0"
+schema_version = 1
+authors = ["Zed Industries <support@zed.dev>"]
+repository = "https://github.com/zed-industries/zed"
+
+[grammars.proto]
+repository = "https://github.com/zed-industries/tree-sitter-proto"
+commit = "0848bd30a64be48772e15fbb9d5ba8c0cc5772ad"

extensions/proto/languages/proto/config.toml

@@ -0,0 +1,13 @@
+name = "Proto"
+grammar = "proto"
+path_suffixes = ["proto"]
+line_comments = ["// "]
+autoclose_before = ";:.,=}])>"
+brackets = [
+    { start = "{", end = "}", close = true, newline = true },
+    { start = "[", end = "]", close = true, newline = true },
+    { start = "(", end = ")", close = true, newline = true },
+    { start = "\"", end = "\"", close = true, newline = false, not_in = ["comment", "string"] },
+    { start = "'", end = "'", close = true, newline = false, not_in = ["comment", "string"] },
+    { start = "/*", end = " */", close = true, newline = false, not_in = ["comment", "string"] },
+]

extensions/proto/languages/proto/highlights.scm

@@ -0,0 +1,61 @@
+[
+  "syntax"
+  "package"
+  "option"
+  "optional"
+  "import"
+  "service"
+  "rpc"
+  "returns"
+  "message"
+  "enum"
+  "oneof"
+  "repeated"
+  "reserved"
+  "to"
+] @keyword
+
+[
+  (key_type)
+  (type)
+  (message_name)
+  (enum_name)
+  (service_name)
+  (rpc_name)
+  (message_or_enum_type)
+] @type
+
+(enum_field
+  (identifier) @constant)
+
+[
+  (string)
+  "\"proto3\""
+] @string
+
+(int_lit) @number
+
+[
+  (true)
+  (false)
+] @boolean
+
+(comment) @comment
+
+[
+  "("
+  ")"
+  "["
+  "]"
+  "{"
+  "}"
+  "<"
+  ">"
+]  @punctuation.bracket
+
+[
+ ";"
+ ","
+] @punctuation.delimiter
+
+"=" @operator

extensions/proto/languages/proto/outline.scm

@@ -0,0 +1,19 @@
+(message
+    "message" @context
+    (message_name
+        (identifier) @name)) @item
+
+(service
+    "service" @context
+    (service_name
+        (identifier) @name)) @item
+
+(rpc
+    "rpc" @context
+    (rpc_name
+        (identifier) @name)) @item
+
+(enum
+    "enum" @context
+    (enum_name
+        (identifier) @name)) @item