"field": synthetic variable creation in accessors, codegen changed accordingly, a set of tests, relevant code fix (j2k)

compiler/testData/diagnostics/tests/backingField/FieldInInterface.txt

@@ -0,0 +1,8 @@
+package
+
+public interface My {
+    public open val x: kotlin.Int = 0
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}