gui: display Mapped AS in peers info window

Summary:

Continuing the asmap integration of PR16702 which added mapped_as to the rpc getpeerinfo output, this adds the mapped AS to the Peers detail window in the GUI wallet.
Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

This is a backport of Core PR18402

Test Plan:
ninja && src/qt/bitcoin-qt

Menu Window -> Peers, select a peer, the "Mapped AS" field is now visible at the bottom of the right widget.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8876