Add Permissions to TestDefinition

[caspervonb]

Would be nice to be able to specify the permissions a test should run in.

Deno.test({
  name: "foo",
  fn() {
    assertThrows(function() {
      Deno.open("...");
    });
  },
  permissions: {
    write: false,
  },
});

To avoid breaking the sandboxing rules, this would not be able to request more permissions than the initial set that was given to deno test but can reset the permission set to that before every test is run.