Start moving wallet and ismine code to scriptpubkeyman.h, scriptpubkeyman.cpp
The easiest way to review this commit is to run:
git log -p -n1 --color-moved=dimmed_zebra
And check that everything is a move (other than includes and copyrights comments).
This commit is move-only and doesn't change code or affect behavior.
Depends on D6998, D7007
Partial backport of Core PR17260