RFR: 8375621: Move RBTree implementation to inline file to minimize included headers [v3]

[Casper Norrbin]

On Thu, 22 Jan 2026 08:52:58 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> 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.
>
> Sort as in outputStream should go after Arena because A < O in the alphabet, is what I reckon Stefan meant.

That makes more sense. Fixed now :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/29295#discussion_r2715937107