Track the active tab and browsing context for devtools (#36168)

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---Part of #35867, per Step 5 suggestion. This PR:
- Adds active_tab (via RefCell) to RootActor, updated in
get_tab_msg_by_browser_id.
- Adds browsing_context() helper to TabDescriptorActor.
- Adds actor()`getter to TabDescriptorActorMsg for  access in root.rs.
-Creates the chain (Root - Tab - BrowsingContext) for routing
colorSchemeSimulation.
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- [X ] `./mach build -d` does not report any errors
- [X ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because they’re structural
setup for the actor chain and don’t change the system's behavior yet.

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---------

Signed-off-by: Uthman Yahaya Baba <uthmanyahayababa@gmail.com>

components/devtools/actors/tab.rs

@@ -43,6 +43,10 @@ impl TabDescriptorActorMsg {
     pub fn browser_id(&self) -> u32 {
         self.browser_id
     }
+
+    pub fn actor(&self) -> String {
+        self.actor.clone()
+    }
 }
 
 #[derive(Serialize)]
@@ -167,4 +171,9 @@ impl TabDescriptorActor {
     pub(crate) fn is_top_level_global(&self) -> bool {
         self.is_top_level_global
     }
+
+    #[allow(dead_code)]
+    pub fn browsing_context(&self) -> String {
+        self.browsing_context_actor.clone()
+    }
 }