RFR: 7509: Add 2021-09 target platform [v3]

[Alex Macdonald]

On Fri, 14 Jan 2022 17:33:45 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> ...also updating babel.
>
> Marcus Hirt has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains six commits:
> 
>  - Merge branch 'master' into 7509-2021-09
>  - Fixed version
>  - 7509: Add 2021-09 target platform
>  - Fixing copyright years
>  - Further project files and fixes
>  - 7505: Fixing project setup

Marked as reviewed by aptmac (Committer).

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PR: https://git.openjdk.java.net/jmc/pull/357