Flip the --incompatible_disallow_set_constructor flag by default

RELNOTES[INC]: `set` is deprecated in BUILD and .bzl files, please use `depset`
instead. Ordering names have also been changed, please use "default",
"postorder", "preorder", and "topological" instead of "stable", "compile",
"naive_link", and "link" correspondingly.

PiperOrigin-RevId: 166830004

src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java

@@ -63,7 +63,7 @@ public class SkylarkSemanticsOptions extends OptionsBase implements Serializable
 
   @Option(
     name = "incompatible_disallow_set_constructor",
-    defaultValue = "false",
+    defaultValue = "true",
     category = "incompatible changes",
     documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
     effectTags = {OptionEffectTag.UNKNOWN},