RFR: 7062: Update to the Eclipse 2020-12 platform

[Marcus Hirt]

On Fri, 18 Dec 2020 19:52:25 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> Yes, as downstream we can select a different release if need be; well it isn't necessarily in our hands with Fedora but anyways.
>
> After playing around a bit more, there seems to be some problem with the Chromium based browser component on Windows when using 2020-12. I'm withdrawing this for now - the big sur fixes will have to wait.

Might want to take this, but keep 2020-09 as a default, for two reasons:

1. It makes it easier for people to try 2020-12 based builds (override with -P2020-12).
2. It uses the most recent babel release.

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PR: https://git.openjdk.java.net/jmc/pull/185