devtools: Fix id collisions by using incrementing counters (#35971)

Devtools clients need a `browserId`, `browsingContextID`, and
`outerWindowID`, which correspond to WebViewId, BrowsingContextId, and
PipelineId in Servo. These u32 values were previously derived from our
sharded (u32,u32) id values by taking only the `index` (second u32) and
ignoring the `namespace_id` (first u32), leading to collisions.

This patch fixes that by mapping those Servo ids to sequential u32
values.

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---------

Signed-off-by: Delan Azabani <dazabani@igalia.com>

components/devtools/actors/watcher.rs

@@ -259,10 +259,9 @@ impl Actor for WatcherActor {
                 ActorMessageStatus::Processed
             },
             "getParentBrowsingContextID" => {
-                let browsing_context_id = target.browsing_context_id.index.0.get();
                 let msg = GetParentBrowsingContextIDReply {
                     from: self.name(),
-                    browsing_context_id,
+                    browsing_context_id: target.browsing_context_id.value(),
                 };
                 let _ = stream.write_json_packet(&msg);
                 ActorMessageStatus::Processed