AG0018 Don't block IReadOnlyCollection<T>

[szaboopeeter]

@szaboopeeter Our team, would like to use IReadOnlyCollection<> which results in quite a bit of warnings. I can update the docs if we agree to allow this.

Originally posted by @inemtsev in #155 (comment)

[szaboopeeter]

@inemtsev Sounds good to me. Personally I don't see any problem in allowing any or all of the System.Collections.Generic interfaces https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic?view=net-5.0#interfaces

[inemtsev]

Totally agree.

[inemtsev]

@szaboopeeter I cloned the project and made the change, but Github doesnt let me push. Do I need some special permissions?

[szaboopeeter]

Easiest way is if you fork it