Created module idea-test-framework and moved classes needed for idea tests there

Moved tests for completion and their test data into module idea-completion

idea/idea-completion/testData/basic/common/InNestedClass.kt

@@ -0,0 +1,23 @@
+class C {
+    val field = 0
+    class NestedClass
+    inner class InnerClass
+
+    class N {
+        fun foo(){
+            <caret>
+        }
+    }
+
+    companion object {
+        fun fromClassObject(){}
+    }
+}
+
+fun C.extensionForC(){}
+
+// ABSENT: field
+// EXIST: NestedClass
+// EXIST: InnerClass
+// EXIST: fromClassObject
+// ABSENT: extensionForC