Retain data flow info after array accesses

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/ArrayGetSetConvention.kt

@@ -0,0 +1,26 @@
+trait G {
+    fun get(x: Int, y: Int): Int = x + y
+    fun set(x: Int, y: Int, value: Int) {}
+}
+
+fun foo1(a: Int?, b: G) {
+    b[a!!, a<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>] = a
+    a : Int
+}
+
+fun foo2(a: Int?, b: G) {
+    b[0, a!!] = a
+    a : Int
+}
+
+fun foo3(a: Int?, b: G) {
+    val r = b[a!!, a]
+    a : Int
+    r : Int
+}
+
+fun foo4(a: Int?, b: G) {
+    val r = b[0, a!!]
+    a : Int
+    r : Int
+}