RFR: 8252600: [JVMCI] update JVMCI code style and mx configuration

[Doug Simon]

On Sat, 17 Apr 2021 20:37:08 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> This PR updates the configuration files used to develop the JVMCI Java and C++ sources with mx and Eclipse.

Until we have downstream repos for JDK 17, it's very handy to have this config in the JDK. I've tried to keep it only in JVMCI related directories so as to not perturb non-JVMCI sources. However, if the consensus is that this config does not belong in the JDK at all, I will repurpose this PR to remove all such config as it's current broken as is.

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PR: https://git.openjdk.java.net/jdk/pull/3559