This removes the bulk of our reliance on the rand crate in non-test
envs, paving a way towards a syscall-less rust-lightning and WASM.
Since this is a breaking change for full_stack_target (and several
fuzz targets), go ahead and make other changes to make things more
distinct.
Peer may send us a shutdown_scriptpubkey in open_channel or
accept_channel messages. Before to enforce this policy on channel
closing, we want to be sure that our peer has opt-in to it.
Extend LocalFeatures new method visibilty from crate to public
for fuzz tests
