Support delivering local image styles until remote upload is complete

I created a MR based on the last patch. I had to fix a bunch of stuff to get it working for me:

• Update deprecated/removed core services and functions
• Fix some small issues that came up
• Fix the temporary image generation failing if an image style changes the extension of the generated derivative

I also opened an MR in the flysystem_gcs project, integrating the new code here in an actual adapter: 🐛 Saving and loading content takes way too long when multiple image styles are used Needs review .

Now both MR's are in a working state, this one still needs tests.

@dieterholvoet Would you be kind enough to change your MR to apply against the 2.1.x-dev branch? I'd like to see if the automated tests will pass, it appears that your MR does apply to 2.1.x as well as 8.x-1.x.

I rebased the branch against 2.1.x, there weren't any conflicts. Changing back to Needs work because there aren't any tests yet - unless you decide that's not necessary.

https://www.drupal.org/pift-ci-job/2730529 →

Existing test coverage appears to be adequate, however this patch does fail one existing tests. In looking at the test it appears that perhaps the test needs to be updated.

Can you take a look at the failing test, determine if the failing assertion on `src/Unit/Routing/FlysystemRoutesTest.php:161` needs to be revised, and submit a revision as part of this MR?

If the assertion is still valid, note that here as well, and we'll need to work on this a bit more.

Fix in version 2.2.x, will need to be ported to 2.3.x+.

Also test coverage will need to be expanded to cover the new classes that have been added.