tests: add a test for a fix of getting an ArraySlice of an CocoaArray

The problem was fixed in 375f289.

rdar://74807247

Author: eeckstein

test/stdlib/objc-array-slice.swift

@@ -0,0 +1,22 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -o %t/a.out
+// RUN: %target-codesign %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+import Foundation
+
+let array = NSMutableArray()
+for _ in 0..<1000 {
+  array.insert(NSObject(), at: 0)
+}
+
+// Check that this does not crash because of an over-release of the array content.
+_ = (array as! [NSObject]).prefix(3)
+_ = (array as! [NSObject]).prefix(3)
+
+// CHECK: done
+print("done")
+