Adds tests for when the connection fails during
1) splice tx_signature
2) splice commitment_signed
Fleshed out the reestablish flow for these two cases and implemented the fixes to make these reestablish flows work.
Part of this work required changing commit process for splices: Now we send a single commit_part for the splice where previously we sent all commits, and accordingly, we no longer revoke in response.
Changelog-Fixed: Implemented splicing restart logic for tx_signature and commitment_signed. Splice commitments are reworked in a manner incompatible with the last version.
