Push Down: Initial Support

idea/testData/refactoring/pushDown/pushInterfaceMembersAndMakeAbstract.kt

@@ -0,0 +1,31 @@
+interface <caret>I {
+    // INFO: {"checked": "true", "toAbstract": "true"}
+    val x: Int get() = 2
+    // INFO: {"checked": "true", "toAbstract": "true"}
+    val y: Int
+    // INFO: {"checked": "true", "toAbstract": "true"}
+    fun foo(n: Int): Boolean = n > 0
+    // INFO: {"checked": "true", "toAbstract": "true"}
+    fun bar(s: String)
+
+    // INFO: {"checked": "true", "toAbstract": "true"}
+    class Y {
+
+    }
+}
+
+abstract class A : I
+
+class B : I {
+    override val y = 1
+
+    override fun bar(s: String) = s.length()
+}
+
+interface J : I
+
+interface K : I {
+    override val y: Int get() = 1
+
+    override fun bar(s: String) = s.length()
+}