refactor: Rename JoinErrors and re-use it

Summary:

scripted-diff: Rename JoinErrors in more general MakeUnorderedList

-BEGIN VERIFY SCRIPT-
sed -i -e 's/JoinErrors/MakeUnorderedList/' -- src/qt/bitcoin.cpp
-END VERIFY SCRIPT-

refactor: Move MakeUnorderedList into util/string.h to make it reusable

refactor: Reuse MakeUnorderedList where possible

This is a backport of core#22653

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18215