Move all basic completion tests to common folder

idea/testData/completion/basic/common/ExtendClassName.kt

@@ -0,0 +1,13 @@
+open class MySecondClass() {
+}
+
+open class MyFirstClass<T> {
+
+}
+
+class A() : My<caret> {
+    public fun test() {
+    }
+}
+
+// EXIST: MySecondClass, MyFirstClass