Mark @:compilerGenerated as internal

Plus, it doesn't seem to be C# / Java specific anymore (it's added in ensure_struct_init_constructor for instance).

src-json/meta.json

@@ -162,7 +162,7 @@
 		"name": "CompilerGenerated",
 		"metadata": ":compilerGenerated",
 		"doc": "Marks a field as generated by the compiler. Should not be used by the end user.",
-		"platforms": ["java", "cs"]
+		"internal": true
 	},
 	{
 		"name": "Const",