Bug 246386

Unfortunately GitHub doesn't support dependent branches for cross-repo PRs, but I think we could support them a bit better on our side.

I frequently end up developing changes that have dependencies on other changes that haven't yet landed. Neither combining them into a single PR, nor just waiting until the previous one has merged are great options.

Running `git webkit pr` on a branch with dependencies mostly works, except that it creates the PR against 'main', so it also includes all the commits from dependent branches. See https://github.com/WebKit/WebKit/pull/4085.

This is somewhat ok, since it means that EWS works. Once the dependent branches have merged, I can just rebase and re-push the PR and the other commits will disappear.

I think ideally we'd skip putting the commit messages from the dependent branch commits into the PR description, and instead include a message to reviewers that those commits aren't (logically) part of this PR and shouldn't be reviewed. Maybe including links to the PRs where those commits can/should be reviewed?

I'm not sure if there's much else we can do to make it clearer on the GitHub review side.

We also get a lot of log spew on the client side when pushing them, looks like parsing of the commit message is failing in some way?