This is likely inherited from bitcoind, and a bit awkward for us, so
we parse it into a classic struct, but serialize it back into the
bitcoind format when talking to the RPC.
We are inferring the field numbers on the fly, which isn't really
compatible with the way GRPC field numbers work, i.e., they must be
stable while the IDL file evolves. So far when a field was added in
the middle of a struct or removed all subsequent fields would get
renumbered, essentially breaking any client that was using the old
scheme.
We now add a meta file `.msggen.json` that keeps track of the numbers
assigned so far, so they can be reused, and new ones can be generated
not to conflict with existing ones. This file is intentionally kept
generic, so other generators can add more information that has to be
managed across runs.
Changelog-None
The server doesn't do much more than unwrapping the request from its
grpc envelope, convert it into the matching JSON-RPC binding struct,
initiate the RPC connection (until we have connection pooling), and
then forwards the converted request. The inverse then happens for the
result.
