Fix use-after free

On CDP.BrowserContext.deinit, clear the isolated world ExecutionContext before
terminating the session. This is important as the isolated_world list is
allocated from the session.arena.

Also, semi-revert 63f1c85964. Before all this
we were running microtasks on ExecutionWorld.removeContext. That didn't seem
right (and I thought it was the original source of the bug). But, for the "real"
Page context, this is critical, since Microtasks can reference the Page object.
Since microTasks are isolation-level, it's possible for a microtasks for Page1
to execute after Page1 goes away (if we create a new page, Page2). This re-adds
the microtask "draining", but only for the Page (i.e. in Page.deinit).

src/cdp/cdp.zig

@@ -411,15 +411,16 @@ pub fn BrowserContext(comptime CDP_T: type) type {
                 transfer.abort(error.ClientDisconnect);
             }
 
+            for (self.isolated_worlds.items) |*world| {
+                world.deinit();
+            }
+            self.isolated_worlds.clearRetainingCapacity();
+
             // If the session has a page, we need to clear it first. The page
             // context is always nested inside of the isolated world context,
             // so we need to shutdown the page one first.
             self.cdp.browser.closeSession();
 
-            for (self.isolated_worlds.items) |*world| {
-                world.deinit();
-            }
-            self.isolated_worlds.clearRetainingCapacity();
             self.node_registry.deinit();
             self.node_search_list.deinit();
             self.cdp.browser.notification.unregisterAll(self);