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/tab.rs

@@ -146,18 +146,15 @@ impl TabDescriptorActor {
 
     pub fn encodable(&self, registry: &ActorRegistry, selected: bool) -> TabDescriptorActorMsg {
         let ctx_actor = registry.find::<BrowsingContextActor>(&self.browsing_context_actor);
-        let browser_id = ctx_actor.browser_id.0.index.0.get();
-        let browsing_context_id = ctx_actor.browsing_context_id.index.0.get();
-        let outer_window_id = ctx_actor.active_pipeline.get().index.0.get();
         let title = ctx_actor.title.borrow().clone();
         let url = ctx_actor.url.borrow().clone();
 
         TabDescriptorActorMsg {
             actor: self.name(),
-            browser_id,
-            browsing_context_id,
+            browser_id: ctx_actor.browser_id.value(),
+            browsing_context_id: ctx_actor.browsing_context_id.value(),
             is_zombie_tab: false,
-            outer_window_id,
+            outer_window_id: ctx_actor.active_outer_window_id.get().value(),
             selected,
             title,
             traits: DescriptorTraits {