[wallet] Rescan abortability

Summary:
Backport core PR10208:
[wallet] Add support for aborting wallet transaction rescans.
[rpc] Add abortrescan command to RPC interface.

Depends on D1726 and D1725

Test Plan:

make check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1727