Add generic interfaces for classes that have no interfaces yet.

[bytes-commerce]

This change introduces Interfaces for final classes.

The reason I am proposing this change is to have the ability to Mock interfaces and without having to rely on some hacky attempts to correctly generate PHPUnit tests.

I've moved from direct declarations in constructors etc to the Interface usage. This also allows for a more dynamic development approach whilst keeping final classes at hand. They still can be decorated. However, with this, its much more strict to work with EasyAdmin as 3rd Party Developer and new contributors are less likely to introduce new classes incorrectly.

I've raised the issue here: #5890 and was redirected to the "No Final" package but its not what I am looking for; instead I look for strict code.

[OskarStark]

If accepted by @javiereguiluz this PR is way to big and not reviewable. We should create a meta issue and do a PR interface by interface

[bytes-commerce]

@OskarStark It should have half the size; in the previous commit there is a change that I made with PHPStorm that changed nearly all files. Even tho so, its roughly 125 files changed and another 125 files added, more or less. Also the reason why I moved it to draft. Its to big to be reviewed comfortably.

[javiereguiluz]

I like the idea of adding some of these missing interfaces ... but I'd prefer to do it slowly. I fear that we're going to break everything by doing this 😞

So, I think we should do this:

• Let's add only 1 interface, make a new release and see how it goes
• I propose to make AdminUrlGeneratorInterface that first interface
• Also, let not add interfaces for DTO objects (this looks like the general approach towards DTOs: https://softwareengineering.stackexchange.com/questions/185636/should-i-create-interfaces-for-data-transfer-objects)

Thanks!

[bytes-commerce]

It should not break anything, but given the size and usage of this project, its much better to do it slowly.

I will create a PR just for the Interface above (as its also the one I need the most at the moment :D).