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.
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Depends on D6998
Partial backport of Core PR17260