Support .NET 7 context behavior

[rockfordlhotka]

Closes #3657

[swegele]

@rockfordlhotka I'm a little confused as to what the new ApplicationContextManagerInMemory is there for (maybe the comments are confusing because it references using HttpContextAccessor but it doesn't actually use that unless I'm missing something).

If a circuit exists then we shouldn't be using HttpContextAccessor because that is not reliable as per MS guidance?

[rockfordlhotka]

Yeah, the comments need updating for sure!

The in-memory type I just added is actually the old context manager from Blazor 6 and 7 (the comments were wrong then too). I just re-added it with a new type name because the new context manager for Blazor 8 doesn't work with older versions of Blazor.

So this is really a temporary thing, until Blazor 6 and 7 go out of support, and then this can be removed (again).