This data structures stores all information necessary for spending a taproot
output (the internal key, the Merkle root, and the control blocks for every
script leaf).
It is added to signing providers, and populated by the tr() descriptor.
These types are equivalent, in data etc, so they need only their
data cast across.
Note a function is used rather than a casting
operator as CKeyID is defined at a lower level than script/standard
Moves all of the various SigningProviders out of sign.{cpp,h} and
keystore.{cpp,h}. As such, keystore.{cpp,h} is also removed.
Includes and the Makefile are updated to reflect this. Includes were largely
changed using:
git grep -l "keystore.h" | xargs sed -i -e 's;keystore.h;script/signingprovider.h;g'
