Add classes.json for type rename migrations

Completed type rename migration following update-17_0_0 pattern:
- Created classes.json with all type renames:
  * Direction → IgxCarouselDirection
  * Size → ElementDimensions
  * IChangeCheckboxEventArgs → IChangeRadioEventArgs
- Migration now uses UpdateChanges.updateClasses()
- Follows established project migration architecture
- Enables automatic type name updates during ng update

This completes the migration script implementation.

Co-authored-by: kdinev <[email protected]>

Author: Copilot

projects/igniteui-angular/migrations/update-21_0_0/changes/classes.json

@@ -0,0 +1,17 @@
+{
+    "$schema": "../../common/schema/class.schema.json",
+    "changes": [
+        {
+            "name": "Direction",
+            "replaceWith": "IgxCarouselDirection"
+        },
+        {
+            "name": "Size",
+            "replaceWith": "ElementDimensions"
+        },
+        {
+            "name": "IChangeCheckboxEventArgs",
+            "replaceWith": "IChangeRadioEventArgs"
+        }
+    ]
+}