This makes a number of changes:
- Get rid of the verification_progress argument in the node interface
NotifyHeaderTip (it was always 0.0).
- Instead of passing a CBlockIndex* in the UI interface's NotifyHeaderTip,
send separate height, timestamp fields. This is becuase in headers presync,
no actual CBlockIndex object is available.
- Add a bool presync argument to both of the above, to identify signals
pertaining to the first headers sync phase.
This is a partial backport of core#25717
https://github.com/bitcoin/bitcoin/pull/25717/commits/376086fc5a187f5b2ab3a0d1202ed4e6c22bdb50
Depends on D15169