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/custom/TopLevelNonImportedExtFunSrc/source.kt

@@ -0,0 +1,9 @@
+package abc
+
+public fun abcdAAA1(): Unit {}
+
+public fun abcdBBB2(i: Int) {}
+
+public fun Int.abcdCCC3() {}
+
+public fun Int.abcdDDD4(i: Int) {}