chancloser: implement the new option_simple_close co-op close flow

[Roasbeef]

We should implement the new restricted chan co-op close flow: lightning/bolts#1096. Details of the new closing flow can be found in the linked PR.

Once this is implemented, it should be using along side the final taproot chans feature bit by default. This gives us a clean way to update to both the finalized version, and also require this new co-op close flow.

Implementation wise, it may make sense to attempt to start from a clean slate (new state machine), so we can get a better feel of the total code surface area of this new variant vs the existing widely implemented co-op close flow.

[ZZiigguurraatt]

Seems like this has been superseded by lightning/bolts#1205 and lightning/bolts#1205 is now implemented in LND?

[Roasbeef]

Yeah you're right, we just never closed this issue after the feature was merged.