Fix VS complaining about missing projects in slns

[ViktorHofer]

Contributes to #65552

These changes contribute to fixing the broken Visual Studio experience when interacting with out-of-band projects, like Microsoft.Extensions.* in solution files.

The changes are grouped by commits:

1. Relevant infrastructure changes to avoid references to inbox only libraries.
2. Update Microsoft.Extensions.* ref projects
3. Update Microsoft.Extensions.* src projects (just cleaning-up the property that doesn't need to be set anymore)
4. Update other out-of-band projects that are referenced by Microsoft.Extensions* projects. I plan to submit an extra PR for the remaining ones that aren't part of the Microsoft.Extensions.* graph as I wanted to keep that out of this PR to keep the change minimal.
5. Update two source files for which an analyzer complained about the missing usage of Span now that System.Memory.dll reaches the compiler.

cc @ericstj as we discussed this in our 1:1 last Thursday.

[ghost]

Tagging subscribers to this area: @dotnet/runtime-infrastructure
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Contributes to #65552

These changes fix the broken Visual Studio experience when interacting with out-of-band projects, like Microsoft.Extensions.* in solution files.

The changes are grouped by commits:

1. Relevant infrastructure changes to avoid references to inbox only libraries.
2. Update Microsoft.Extensions.* ref projects
3. Update Microsoft.Extensions.* src projects (just cleaning-up the property that doesn't need to be set anymore)
4. Update other out-of-band projects that are referenced by Microsoft.Extensions* projects. I plan to submit an extra PR for the remaining ones that aren't part of the Microsoft.Extensions.* graph as I wanted to keep that out of this PR to keep the change minimal.
5. Update two source files for which an analyzer complained about the missing usage of Span now that System.Memory.dll reaches the compiler.

cc @ericstj as we discussed this in our 1:1 last Thursday.

Author:	ViktorHofer
Assignees:	ViktorHofer
Labels:	area-Infrastructure
Milestone:	-

[eerhardt]

LGTM. Thanks for this cleanup!

[ericstj]

This LGTM. Seems like we should have docs somewhere that describe how to maintain references in project files based on various criteria. Do we need to update those?

[ViktorHofer]

We have project docs which are probably the right place to encode rules for references. I will submit a PR to update them.