Make the memory reporting multi-process aware (#35863)

So far the memory reporter aggregates reports from all processes, and
runs the system reporter only in the main process. Instead it is
desirable to have per-process reports. We do so by:
- creating a ProcessReports struct that holds includes the pid in
addition to the reports themselves.
- running the system memory reporter also in content processes.
- updating the about:memory page to create one report per process, and
add useful information like the pid and the urls loaded in a given
process.

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---
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- [X] `./mach build -d` does not report any errors
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![image](https://github.com/user-attachments/assets/0bafe140-539d-4d6a-8316-639309a22d4a)

Signed-off-by: webbeef <me@webbeef.org>

components/constellation/constellation.rs

@@ -712,7 +712,7 @@ where
                     // namespace 0 for the embedder, and 0 for the constellation
                     next_pipeline_namespace_id: PipelineNamespaceId(2),
                     time_profiler_chan: state.time_profiler_chan,
-                    mem_profiler_chan: state.mem_profiler_chan,
+                    mem_profiler_chan: state.mem_profiler_chan.clone(),
                     phantom: PhantomData,
                     webdriver: WebDriverData::new(),
                     document_states: HashMap::new(),
@@ -739,7 +739,7 @@ where
                     active_media_session: None,
                     rippy_data,
                     user_content_manager: state.user_content_manager,
-                    process_manager: ProcessManager::new(),
+                    process_manager: ProcessManager::new(state.mem_profiler_chan),
                 };
 
                 constellation.run();