RFR: 1216: Update to JDK 17 and Gradle 7.2

Wed Oct 13 20:53:24 UTC 2021

On Wed, 13 Oct 2021 18:13:41 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> This patch bumps the required JDK version to build and run Skara to JDK 17 and the version of Gradle to 7.2. I'm also eliminating some redundant declarations of where to download the JDK binaries so that it's all defined in deps.env.

Marked as reviewed by ihse (Reviewer).

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PR: https://git.openjdk.java.net/skara/pull/1235