Fix local and global uninitialized array access (#2816)

* Fix uninitialized array access/initialization

* Handle printing uninitialized value

* Fix error message directory name

explorer/testdata/array/uninitialized_local_array_access.carbon

@@ -0,0 +1,18 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: 100
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  var my_array : [i32; 1];
+  my_array[0] = 100;
+  Print("{0}", my_array[0]);
+  return 0;
+}