#2378: update .clang-format to match style guidelines

[cz4rs]

fixes #2378

• update our .clang-format file to better match project's style guidelines
• add a CI check to run clang-format on the PR changes and post a comment with the output (see #2378: update .clang-format to match style guidelines #2379 (comment) for an example)

The new PR checks (clang-format) workflow will NOT fail when the style is not applied, for now this is purely informative.

---

Misc notes:

• Official style guidelines: https://github.com/DARMA-tasking/vt/wiki/Code-Style-Guidelines
• It is possible to disable formatting for a section of code with:

// clang-format off
...
// clang-format on

[cz4rs]

887 files changed looks somewhat scary, but a lot of those changes are pretty innocent - adding missing spaces, adjusting line length etc. I will try to identify the key and potentially controversial changes (for example all serialize methods formatting gets much less readable).

[cz4rs]

Meeting notes: consider only running clang-format for recent changes (current PR) and adding comments / reporting in CI.

[github-actions]

clang-format output for this changeset:

no modified files to format

[cz4rs]

git clang-format-16 --diff origin/${{ github.base_ref }} || true is the core of the action, the rest is pretty much boilerplate and comment-posting code.

[lifflander]

Makes sense!

[cz4rs]

This script part boils down to:

• find the comment id if the comment already exists
• create or update the comment with clang-format output

[cz4rs]

This is pretty much the same what DARMA-tasking/comment-on-pr action does, but the script seems short enough to be put directly here.

[lifflander]

Looks great to me.