The current stable branch is determined based on the current version mapped to
the npm `latest` tag (by replacing the patch version number with 'x' - e.g.
`1.2.3` --> `1.2.x`).
PRs against the stable branch will be deployed to the preview server (as long as
the rest of the requirements are met). Commits on the stable branch itself will
be deployed to production.
Fixes#16908
Previously, PR previews were deployed after successfully running all tests.
While this makes sense for staging/production deployments, previews should be
available as soon as possible (and regardless of the outcome of tests).
Fixes#16705
Previously, no previews would be deployed for PRs that didn't touch files inside
`aio/`. Now, previews will be deployed for PRs that touch non-spec files inside
either `aio/` or `packages/` (as long as other preconditions are met).
Partially addresses #16526.