Simple multi-cast, multi-channel communication foundation layer (alternative)

What does this MR do and why?

For #358899 (closed)

What

This is an emergency backup implementation for a multi-cast, multi-channel communication harness.
This specific implementation uses emulates the RxJS Subject API (as the gold standard), but ultimately doesn't do anything special for the multi-cast implementation. The other option uses RxJS Subjects, which is much more code (until version 8, when it may be able to import significantly fewer parts), but with that larger implementation also comes substantially better data stream management should more nuanced use-cases arise.

This MR should not be considered a viable alternative unless the RxJS solution is considered an impossible addition. The RxJS solution is much better, more robust, with testing tools and a wide ecosystem of integrations and examples. It also matches proposed language specifications, which may help smooth transitions to native language features.

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