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/multifile/ExtensionOnNullable/ExtensionOnNullable.dependency.kt

@@ -0,0 +1,14 @@
+package second
+
+fun String.helloFun() {
+}
+
+fun String.helloWithParams(i : Int) : String {
+    return ""
+}
+
+fun String.helloFunPreventAutoInsert() {
+}
+
+fun Int.helloFake() {
+}