add $options and $headers parameters to HttpKernelUiHelperTrait::drupalGet()

Headers behave interestingly.

Mink's BrowserKitDriver::setRequestHeader() does this:

        $name = str_replace('-', '_', strtoupper($name));

so headers are in ALL_CAPS.

And then when the request comes into the HTTP kernel, symfony's HeaderBag in the request does this:

        $key = strtr($key, self::UPPER, self::LOWER);

The effect is that no matter what case your header name is in, it ends up in all lower case.

Applied suggestions.

I've moved common helpers to a new trait. That should make the diff easier to read, as it means that the new Kernel test is a smaller class, and it should be clear that the methods that have moved to UpdateTestAssertionsTrait are exact copies from UpdateTestBase.

Also, when reviewing, it'll make it clearer what changes from Functional -> Kernel if you diff against the FIRST commit of the branch, rather than main. That's because the first commit I made was JUST the file copy of UpdateContribTest.php (commit message 'copy browser test', currently SHA dde55743f25cffc55453fd0b353bedabed98c413). So diffing to that shows you the changes that have to be made for it to run as a Kernel test, and you can see clearly that there's some new setup stuff, and then the actual tests are identical apart from some drupalGet() calls (those are needed because we no longer run the batch UI, so we don't get automatically taken to a refreshed update page).

However -- I can't get gitlab to show me this, so might be a CLI only thing :(

There was already coverage in KernelTestHttpRequestTest, but I've added coverage of a Url object with options.

I'm not sure we even need a CR update? https://www.drupal.org/node/3502609 doesn't need to cover every single parameter to the new drupalGet().

It actually already says this (oops!):

> The test trait \Drupal\Tests\HttpKernelUiHelperTrait provides methods drupalGet(), clickLink(), and assertSession() which work the same way as the corresponding methods in the test trait Drupal\Tests\UiHelperTrait for Browser tests.