Data Inflow: Show composite assignments

#KT-19112 Fixed

idea/testData/slicer/inflow/compositeAssignments.kt

@@ -0,0 +1,9 @@
+// FLOW: IN
+
+fun <caret>assignmentWithSum(n: Int): Int {
+    var result = 0
+    result += n
+    result++
+    --result
+    return result
+}

idea/testData/slicer/inflow/compositeAssignments.results.txt

@@ -0,0 +1,8 @@
+3 fun <bold>assignmentWithSum(n: Int): Int {</bold>
+8 	return <bold>result</bold>
+4 		var <bold>result = 0</bold>
+4 			var result = <bold>0</bold>
+5 			<bold>result += n</bold>
+6 			<bold>result++</bold>
+4 				DUPLICATE: var <bold>result = 0</bold>
+7 			<bold>--result</bold>