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/common/BackingFieldsInStringTemplate.kt

@@ -0,0 +1,15 @@
+class C {
+    var property1 = "abc"
+        get() = $property1 + 1
+    var property2 = "abc"
+        get() = $property2 + 1
+
+    fun foo(){
+        "${$<caret>}"
+    }
+}
+
+// EXIST: $property1
+// EXIST: $property2
+// ABSENT: property1
+// ABSENT: property2