Auto merge of #17269 - gterzian:remove_compositor_forwarding_code_and_use_dedicated_mechanism, r=asajeffrey

Remove compositor forwarding code and use dedicated mechanism

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@paulrouget Here is a first sketch of the proposed "design", handling a first message as a proof of concept, if you could please already take a look before I move all the messages(or method calls) across... thanks

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #15934 (github issue number if applicable).

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