Split analyzers and code fix providers into different assemblies (but same package)

[roji]

We have both code fixes in analyzers in the same assembly, which is something that shouldn't be done (see RS1038); our first code fix was added in #30835, and the reference to Microsoft.CodeAnalysis.Workspaces was added in that PR (/cc @DoctorKrolic).

In #34637 we upgraded to Microsoft.CodeAnalysis 4.13.0, at which point RS1038 started getting reported - it is currently suppressed.

We need to do some build work to have separate projects/assemblies for analyzers and code fixes, but pack them together into the same Microsoft.EntityFramework.Analyzers nuget pacakge. Note dotnet/runtime#88701 which tracks the same for .NET interop analyzers/codefix.

[AndriySvyryd]

Find the case where this causes an error so it can be validated afterwards.