Root-level cascading values + CascadingAuthenticationState at root

[SteveSandersonMS]

Implements #49104
Fixes #48927

See #49104 for the design. This PR includes a root-level equivalent to <CascadingAuthenticationState> and E2E tests showing it works in full-stack Blazor with an interactive @page component.

[javiercn]

Looks pretty straightforward.

Since this is meant to handle the CascadingAuthenticationState, do you think we should flow the Principal automatically from static->interactive?

With this fix, you get the cascading authentication state on the server, but you won't get nothing in webassembly, will you?

[SteveSandersonMS]

With this fix, you get the cascading authentication state on the server, but you won't get nothing in webassembly, will you?

TBH I'm not certain it's desirable to make the WebAssembly app think it has a particular authentication state that it didn't obtain itself. For example it could be misleading since the server may consider the WebAssembly app to have a different authentication state (different claims, at the very least) than existed during SSR.

But either way, I think that should be considered out of scope for this PR. This PR is about providing a way that authentication state can be cascaded (once you have established some authentication state), rather than trying to solve other end-to-end problems about how the authentication state is determined in the first place.