[FIR-TEST] Add new testdata generated after changes in previous commit

compiler/testData/diagnostics/testsWithStdLib/purelyImplementedCollection/arrayListNullable.fir.kt

@@ -0,0 +1,23 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+// !WITH_NEW_INFERENCE
+import java.util.*
+
+fun bar(): String? = null
+
+fun foo() {
+    var x = ArrayList<String?>()
+    x.add(null)
+    x.add(bar())
+    x.add("")
+
+    x[0] = null
+    x[0] = bar()
+    x[0] = ""
+
+    val b1: MutableList<String?> = x
+    val b2: MutableList<String> = x
+    val b3: List<String?> = x
+
+    val b4: Collection<String?> = x
+    val b6: MutableCollection<String?> = x
+}