Start doing more validation of intrinsics: assert, new, delete, rand (#2766)

This is adding more validation of intrinsics. It addresses a bug in rand where CHECK-fails would occur for bad range inputs, instead of a runtime error. I'm also addressing what I think was an int32 range issue in the handling by running the generator with int64.

explorer/testdata/assert/assert.carbon

@@ -0,0 +1,15 @@
+// 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: result: 0
+
+package ExplorerTest api;
+
+fn Main() -> i32 {
+  Assert(true, "HALLO WELT");
+  return 0;
+}