codegen-java/kotlin: Fix generation of hashCode methods (#802)

codegen-java:
- use `pattern.pattern()` instead of `pattern` in hashCode method
  (consistent with equals method)

codegen-kotlin:
- use `regex.pattern` instead of `regex` in hashCode method
  (consistent with equals method)
- if a data class has a Regex property, generate not only
  an equals method but also a hashCode method

pkl-codegen-java/src/test/resources/org/pkl/codegen/java/PropertyTypes.jva

@@ -306,7 +306,7 @@ public final class Mod {
       result = 31 * result + Objects.hashCode(this.container);
       result = 31 * result + Objects.hashCode(this.container2);
       result = 31 * result + Objects.hashCode(this.other);
-      result = 31 * result + Objects.hashCode(this.regex);
+      result = 31 * result + Objects.hashCode(this.regex.pattern());
       result = 31 * result + Objects.hashCode(this.any);
       result = 31 * result + Objects.hashCode(this.nonNull);
       result = 31 * result + Objects.hashCode(this._enum);