These files change infrequently, and not much header shuffling is required.
We don't add everything in src/util/ yet, because IWYU makes some
dubious suggestions, which I'm going to follow up with upstream.
Since the removal of NODISCARD in 81d5af42f4,
the only attributes def is LIFETIMEBOUND, and it's included in many more
places that it is used.
This removes all includes which do not have an associated use of LIFETIMEBOUND,
and adds it to the following files, due to their use of the same:
* src/validationinterface.h
* src/script/standard.h
Creates new files util/bip32.h and util/bip32.cpp for containing
BIP 32 stuff.
Moves FormatKeyPath from descriptor.cpp to util/bip32.
Adds a wrapper around it to prepent the 'm' for when just the
BIP 32 style keypath is needed.
