Contribute: update style guide to google + (minimal) exceptions

[tstastny]

Updates style guide documentation with link to google, and out lines our exceptions.

@MaEtUgR @dagar please let me know if I got something wrong.

We would probably also want to add something about clang format / tidy once that's all up and running. But for now this at least gives the general direction what we're trying to move to.

Let me know what you think ;)

NOTE: clang format will be used where astyle was before, we will need to remember to update this doc with instructions for e.g. the hook setup and auto formatting make command (does it stay the same? make format ?) @MaEtUgR @hamishwillee
^see PX4/PX4-Autopilot#19855

[MaEtUgR]

I had some minor comments. Otherwise it's good and like we discussed.
We need to transition with a good strategy. I agree that having the rules should be the first step. We can still slightly adapt them if it's really unavoidable but otherwise just apply them more and more.

[hamishwillee]

Nice. So we're no longer defining our coding standard by a tool (astyle)? If there is a toolchain that manages this it would be good to at least mention it. And if the intent is that clang will do it one day then putting that in a note with a link to the issue PR in which that is addressed would be even better - because it allows easier later cleanup.

Do we need to say something specific about a dislike for magic numbers?

@dagar LGTM - if you're happy just merge.

[tstastny]

Do we need to say something specific about a dislike for magic numbers?

Added :)

So we're no longer defining our coding standard by a tool (astyle)? If there is a toolchain that manages this it would be good to at least mention it. And if the intent is that clang will do it one day then putting that in a note with a link to the issue PR in which that is addressed would be even better - because it allows easier later cleanup.

Yes clang format is intended to take this over (and eventually clang tidy doing even more heavy lifting) - I added a note/link in the PR description. @MaEtUgR if you think we could already add something about this to this document - please feel free to commit directly to this PR.

NOTE: clang format will be used where astyle was before, we will need to remember to update this doc with instructions for e.g. the hook setup and auto formatting make command (does it stay the same? make format ?) @MaEtUgR @hamishwillee
^see PX4/PX4-Autopilot#19855

[hamishwillee]

Thanks @tstastny

This looks good to me. I'm going to merge and we can iterate.

I added you and @MaEtUgR as owners for adding clang update when that is ready: #1927