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

We have both code fixes in analyzers in the same assembly, which is something that shouldn't be done (see [RS1038](https://github.com/dotnet/roslyn-analyzers/blob/main/docs/rules/RS1038.md#other-extension-points)); 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 https://github.com/dotnet/runtime/issues/88701 which tracks the same for .NET interop analyzers/codefix.