Orchardcore testing

[MichaelPetrinolis]

Extract reusable testing assets to an OrchardCore.Testing library

closes #11865

[MichaelPetrinolis]

@Skrypt I wrote the readme as a placeholder ;) - if the PR is to be accepted, we should enrich it with some guidelines and examples on how to use it for unit/integration testing.

[Skrypt]

Ok, no problem. It was a draft, I often do that too. 😉

[hyzx86]

Great !!
Maybe we can add some workflow related tests,

Test code for liquid / jint, such as JSON serialization

[hishamco]

Thanks for your initiative @MichaelPetrinolis, this could be closed - if you don't mind - in favour of #13018

[MichaelPetrinolis]

Thanks for your initiative @MichaelPetrinolis, this could be closed - if you don't mind - in favour of #13018

Sure, no problem, I paused this PR anyway, I used it in my projects but as long as there is the #13018 , I will adjust my code when this gets merged :) Thank you for taking over.