[5.3] Added Container::getFactory() method

[guiwoda]

Without the BC change that #15414 proposed.

[GrahamCampbell]

Please apply my earlier comments.

[guiwoda]

This doesn't avoid the fact that this interface would really need to be added to the contract

We can add it later. There's plenty of implementation code without the proper contract in the rest of the framework. I even made a PR about that a gazillion years ago.

I'll amend with the CS fixes.

[GrahamCampbell]

There's plenty of implementation code without the proper contract in the rest of the framework.

Yeh, I know. That's really unfortunate. I'm just trying to avoid making things worse. :)

[guiwoda]

@GrahamCampbell if this is merged, I can PR the BC change in the Container contract to master 😄

[GrahamCampbell]

Thanks for making those changes. I'd personally rather it only went to master, but I can see arguments for it going to 5.3 in this way too. Ultimately, Taylor will decide if he wants to merge this PR. :)

[guiwoda]

Awesome!
I feel this could be a starting point for decoupling other components from the container. I don't have a strong opinion on 5.3 or 5.4 other than a more immediate availability on projects.