Closes #6724 (Allows object evaluation in devtools)

The purpose of this is to fix how objects were previously evaluated in
the developer tools.

- Before this, evaluating an object such as the `window` would `panic!`
- After this, evaluating an object such as the `window` outputs `[object
  Window]`

A few things to note:

- This commit contains `unsafe` code.
- This does not contain a test because the developer tools cannot be properly tested until #5971 lands.

components/devtools/lib.rs

@@ -40,6 +40,7 @@ use actors::console::ConsoleActor;
 use actors::network_event::{NetworkEventActor, EventActor, ResponseStartMsg};
 use actors::framerate::FramerateActor;
 use actors::inspector::InspectorActor;
+use actors::object::ObjectActor;
 use actors::root::RootActor;
 use actors::tab::TabActor;
 use actors::timeline::TimelineActor;
@@ -68,13 +69,14 @@ mod actor;
 mod actors {
     pub mod console;
     pub mod framerate;
-    pub mod memory;
     pub mod inspector;
+    pub mod memory;
+    pub mod network_event;
+    pub mod object;
     pub mod root;
     pub mod tab;
     pub mod timeline;
     pub mod worker;
-    pub mod network_event;
 }
 mod protocol;