Customizable views area handlers ids

I added a rough proof of concept which works ok.

I had to add the Method Drupal\views\Plugin\views\area\AreaPluginBase::submitOptionsForm() has no return type specified. phpstan error to the list of ignored errors in core/.phpstan-baseline.php since \Drupal\views\Plugin\views\area\Entity already implements it and would break.

I would be against doing this in Drupal core, it adds more options to the Views UI which is already too full of options, and this feel very much like an edge case. If you need this in a project you can just add a custom area plugin that does this and use that, right? Just my feeling.

Back to needs work for the tests.

My rationale for adding this to core would be that almost every other machine name in Drupal can be customized from the UI.