Setup overridability rules for properties built on Java fields

- They overrides each other
- They do not overrides Kotlin propeties and vice versa

core/descriptor.loader.java/src/META-INF/services/org.jetbrains.kotlin.resolve.ExternalOverridabilityCondition

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+org.jetbrains.kotlin.load.java.FieldOverridabilityCondition

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/FieldOverridabilityCondition.kt

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+/*
+ * Copyright 2010-2015 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.load.java
+
+import org.jetbrains.kotlin.descriptors.CallableDescriptor
+import org.jetbrains.kotlin.descriptors.PropertyDescriptor
+import org.jetbrains.kotlin.resolve.ExternalOverridabilityCondition
+
+class FieldOverridabilityCondition : ExternalOverridabilityCondition {
+    override fun isOverridable(superDescriptor: CallableDescriptor, subDescriptor: CallableDescriptor): Boolean {
+        if (subDescriptor !is PropertyDescriptor || superDescriptor !is PropertyDescriptor) return true
+
+        return subDescriptor.isJavaField == superDescriptor.isJavaField
+    }
+
+    // Currently getter is null iff it's loaded from Java field
+    private val PropertyDescriptor.isJavaField: Boolean
+        get() = getter == null
+}