RFR: 1216: Update to JDK 17 and Gradle 7.2

Wed Oct 13 18:20:15 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.

Many projects "happen to work" when using JDK 17 with gradle 7.2, but it isn't supported until gradle 7.3, which is not yet released. See gradle/gradle#16857

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