Change retention of @Property annotation from SOURCE to CLASS:

- it makes it consistent with `@ObjectiveCName` annotation which is also `CLASS`,
- it's necessary for J2CL to read this annotation from `.class` files.

PiperOrigin-RevId: 854091995

Author: micapolos-google

annotations/src/main/java/com/google/j2objc/annotations/Property.java

@@ -70,7 +70,7 @@
  * @author Harry Cheung
  */
 @Documented
-@Retention(RetentionPolicy.SOURCE)
+@Retention(RetentionPolicy.CLASS)
 @Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE})
 public @interface Property {