RFR: 8375621: Move RBTree implementation to inline file to minimize included headers [v2]

[Casper Norrbin]

On Mon, 19 Jan 2026 12:36:08 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Casper Norrbin has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   feedback fixes
>
> src/hotspot/share/utilities/rbTree.hpp line 68:
> 
>> 66: class outputStream;
>> 67: class Arena;
>> 68: class ResourceArea;
> 
> Brownie points if you also sort the forward declarations.

The forward declarations are required by the Arena/ResourceArea allocator classes, so they would need to stay as it is currently. Since all definitions are in `rbTree.hpp`, we need to keep them for now. We could perhaps split up the various tree variants into a separate file, but I feel that would be out of scope here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29295#discussion_r2705114757