Ability to run Blazor Server and WebAssembly components side-by-side in the same document

[MackinnonBuck]

As part of the "Full stack web UI with Blazor" effort, one of our goals is having the ability to interleave Blazor WebAssembly and Server components in the same page, e.g., have a Server component render a WebAssembly component or vice versa. One critical aspect of this feature is allowing Blazor Server and WebAssembly components to coexist on the same page in the first place.

Part of this work will include:

• Updating Blazor's JS API to take into account the possibility of multiple .NET runtimes being available. For example, we would need to resolve ambiguities around where JS->.NET invocations run when WebAssembly and Server runtimes are both available.
• Allowing Blazor Server/WebAssembly functionality to be initialized and disposed on demand. For example, if all Blazor Server components get removed from the page, we would have the option to shut down the circuit and spin it back up later if a Server component gets rendered again.

A deliberate non-goal is allowing completely separate Blazor apps to exist on the same page and behave in isolation. That piece of work is tracked separately in #38128 and addresses different use cases.

[MackinnonBuck]

Closing this as completed in #48294. Follow-up items will be addressed as part of #48396.