[LINTER] Switch to clang-format 10

Summary:
It becomes more difficult to install the older clang-format-8 on recent
systems. Even recent Ubuntu are no longer supported.

Depends on D9740.

Test Plan:

arc lint --everything

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9741