Bump to clang-11 and clang-format-11

Summary:
This bumps the clang CI version as well as the clang-format linter. We keep both in sync so we prevent inconsistency hazard especially with clang-tidy.

The clang-format update introduce a couple changes:

• nested ternary operators are now aligned by the colon character
• Variadic template ellipses have no space anymore, which requires a change to the lint-format-strings.py false positive list.

Depends on D11105.

Test Plan:
With Clang:

ninja all check

arc lint --everything

Run the CI builds for the sanitizers.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11106