RFR: 8273439: Fix G1CollectedHeap includes and forward declarations

[Kim Barrett]

On Tue, 7 Sep 2021 15:40:28 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   can I have reviews for this change that
>   * removes unnecessary includes (just one actually)
>   * removes unnecessary forwards (either not used, or already covered by the #include declaration)
>   * sorts the forward declarations
>   * adds necessary forwards that were not directly included
> 
> Testing: building on various platforms
> 
> Thanks,
>   Thomas

Looks good.

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Marked as reviewed by kbarrett (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5393