LibWeb+LibWebView+WebContent: Add an about:processes page

The intent is that this will replace the separate Task Manager window.
This will allow us to more easily add features such as actual process
management, better rendering of the process table, etc. Included in this
page is the ability to sort table rows.

This also lays the ground work for more internal `about` pages, such as
about:config.

Services/WebContent/WebContentClient.ipc

@@ -108,4 +108,6 @@ endpoint WebContentClient
     did_find_in_page(u64 page_id, size_t current_match_index, Optional<size_t> total_match_count) =|
 
     request_worker_agent(u64 page_id) => (IPC::File socket) // FIXME: Add required attributes to select a SharedWorker Agent
+
+    update_process_statistics(u64 page_id) =|
 }