Vendor buildpack-stdlib

[edmorley]

Since:

• The buildpack-stdlib repo has been sunset/archived, so no future changes to it are expected.
• It's a script rather than a binary and is a small file, so a great candidate for vendoring.
• Downloading it at runtime causes more potential failures modes, as seen in this build failure that blocked the publishing of heroku/builder-classic:22 until it was retriggered: https://app.circleci.com/pipelines/github/heroku/pack-images/1866/workflows/b9fb14a2-04b6-4dbe-b077-927cde11012b/jobs/38937

GUS-W-11283397.

[edmorley]

@Malax Presuming you're fine with this change (to improve reliability of our builder release process), I guess we should also make the same change to these (I'm happy to open PRs for these too, unless you wanted to take it): https://github.com/heroku/heroku-buildpack-java/blob/a963657a19f69960c1a043b24eaf2c7bf7bcc94a/lib/common.sh#L4 https://github.com/heroku/heroku-buildpack-gradle/blob/4743c9418d2116326d8419bd48b1d15ee1e86db6/lib/common.sh#L3 https://github.com/heroku/heroku-buildpack-scala/blob/e9801a34739e51546c51f78c6ea7b810e62e83d2/lib/common.sh#L3

[Malax]

Yeah, I think this makes sense! 👍🏻