Fix inconsistencies and grammar in various files

Summary:
Backport of core PR10680
https://github.com/bitcoin/bitcoin/pull/10680/files

Test Plan:
Read the docs.

arc lint --everything

Reviewers: #bitcoin_abc, deadalnix, nakihito

Reviewed By: nakihito

Subscribers: nakihito

Differential Revision: https://reviews.bitcoinabc.org/D3404