Feature: real OTBR and RCP support - tracking PRs

[EskoDijk]

This issue is to track progress and PRs for the feature of supporting "real" OTBRs in the simulator; and supporting RCP/NCP nodes. The overall benefit is that real devices on the Ethernet/Wi-Fi network such as mobile phones or Thread Border Routers can communicate with the simulated Thread Border Router and its simulated Thread network as if it were a real BR/network.

Support for RCP/NCP nodes in OTNS

• [cli] provide default 'APP' log output implementation in CLI module; allow 'APP' log in Posix app ot-cli openthread#12309 - enables the Posix NCP to send its logs and OTNS status pushes via stdout pipe directly to OTNS.
• [otns] add default (weak) OTNS platform API implementation in core openthread#12308 - enables the Posix NCP CLI app to send OTNS status push messages.
• [cli] joiner start to use correct VendorInfo data openthread#12332 - enables OTNS tests that use 'joiner start' to pass when using the latest openthread repo code.
• [all] support for OT Posix node with RCP using realtime UART #740 - enables RCP nodes in OTNS in the "real-time" mode.

Support for the local host itself to act as OTBR for a network of simulated nodes

• TBD - no PR yet; should be based on above code category once integrated.

Support for creating new node types (RCP, real OTBR, ...) in the GUI

• TBD - should be based on directly above code category once integrated.

Support for OTBR Docker nodes (i.e. no requirement to build/change the local host into an OTBR)

• TBD - consider if useful after previous functions all working.

Working / draft PRs - not directly planned for merging

• Allow running OT-BR attached to a simulated RCP. #711 - the basis for all of the new functionality, code is used for other PRs.
• WIP: pr-real-uart-2 EskoDijk/ot-ns#189 - working branch for generic RCP support including tests.
• [all] Support for RCP+Host, with real-time UART via stdin/stdout, and simplify code EskoDijk/ot-ns#188 - older working branch that also removes some unused Go code ; and clarifies internal dispatcher scheduling events - that could go into a separate PR out of scope of this work.