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/codeFragmentInLibrarySource/customLibrary/customLibrary.kt

@@ -0,0 +1,8 @@
+package customLibrary
+
+public fun foo(parameter: Int): Int {
+    return 1
+}
+
+private fun Int.extOnInt() {
+}