Description of the need

It'd be nice to add an automation (GitHub Action) that formats code nicely for us in PRs. This'd not only make sure code is easy-to-read and consistent, but would prevent the back-and-forth, nit-picky reviews where we ask contributors to add some whitespace here, fix this comment to not overflow 80 characters, etc.

Proposed solution

As discussed in https://github.com/backdrop/backdrop-issues/issues/2785#issuecomment-108..., code linters seem to be moving away from 'stylistic' changes and just focusing on flagging/fixing bugs in code. In other words, a linter will warn you about a missing parentheses, but it won't flag whitespace or line-length issues.

This is where code formatters (or 'prettifiers') come in. I recommend we decide on which we'd like to use and then set it up as a GH action to run on PRs.

Alternatives that have been considered

We can always stick with our current system of having a documented coding style, and pointing contributors to that when we mark their PRs as 'needs work', but I don't think that's an ideal solution for reasons I'll get into below...

Draft of feature description for Press Release (1 paragraph at most)

Backdrop now automatically flags and/or fixes code formatting issues in pull requests for readability and consistency.

Related: * #5245 * #2785

GitHub Link: 
https://github.com/backdrop/backdrop-issues/issues/5568
GitHub Issue #: 
5568