Merge pull request #2871 from dunxen/2024-02-msgcommonfields

Combine common fields for OpenChannel and AcceptChannel V1 & V2

diff --cc lightning/src/ln/channel.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge

diff --cc lightning/src/ln/functional_tests.rs
Simple merge

diff --cc lightning/src/ln/peer_handler.rs
Simple merge

diff --cc lightning/src/ln/shutdown_tests.rs
Simple merge