Move all basic completion tests to common folder

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

@@ -0,0 +1,12 @@
+class Expr {}
+class Num : Expr() {
+    fun testing() {}
+}
+
+fun eval(e : Expr) {
+    if (e is Num) {
+        return e.<caret>()
+    }
+}
+
+// EXIST: testing