Initial implementation of KT-5955 Completion for override methods

#KT-5955 Fixed

idea/idea-completion/testData/basic/common/override/InConstructorParameters.kt

@@ -0,0 +1,22 @@
+interface I {
+    fun foo()
+    val someVal: Int
+    var someVar: Int
+}
+
+class Base1 {
+    protected open fun bar(){}
+    open val fromBase: String = ""
+}
+
+open class Base2 : Base1() {
+}
+
+class A(overr<caret>) : Base2(), I
+
+// EXIST: { lookupString: "override", itemText: "override" }
+// EXIST: { itemText: "override val someVal: Int", tailText: null, typeText: "I" }
+// EXIST: { itemText: "override var someVar: Int", tailText: null, typeText: "I" }
+// EXIST: { itemText: "override val fromBase: String", tailText: null, typeText: "Base1" }
+// EXIST_JAVA_ONLY: { lookupString: "override", itemText: "override: Override" }
+// NOTHING_ELSE