lang: Add autoedge and autogroup meta params to mcl

These weren't yet exposed in mcl. They're now available under the same
Meta namespace as the normal meta param structs. Even though they live
as a separate trait, they should be exposed together for a consistent
interface in mcl. If autoedge or autogroup ever grow additional params,
we can always add: `Meta:autoedge:something` to break it down further.

docs/language-guide.md

@@ -227,6 +227,7 @@ file "/tmp/f1" {
 
 	Meta:noop => true,
 	Meta:delay => $b ?: 42,
+	Meta:autoedge => false,
 }
 ```
 
@@ -250,6 +251,8 @@ file "/tmp/f1" {
 		limit => 4.2,
 		burst => 3,
 		sema => ["foo:1", "bar:3",],
+		autoedge => true,
+		autogroup => false,
 	},
 }
 ```