Auto merge of #14612 - szeged:connect-disconnect-update, r=jdm

Updating GATTServer's  Connect/Disconnect calls

<!-- Please describe your changes on the following line: -->
Added the missing [Step 5.2.3](https://github.com/servo/servo/compare/master...szeged:connect-disconnect-update#diff-1dbe29f87740f5aec93f37adbecace6cR213) to the `connect` function.
Updated the [disconnect](https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetoothremotegattserver-disconnect) function to its current state in the specification, including the `clean_up_disconnected_device` and the `garbage_collect_the connection` functions.
Added new tests for checking the invalid state of JS objects after disconnection.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/14612)
<!-- Reviewable:end -->

components/script/dom/bluetooth.rs

@@ -104,6 +104,10 @@ impl Bluetooth {
         self.global().as_window().bluetooth_thread()
     }
 
+    pub fn get_device_map(&self) -> &DOMRefCell<HashMap<String, MutJS<BluetoothDevice>>> {
+        &self.device_instance_map
+    }
+
     // https://webbluetoothcg.github.io/web-bluetooth/#request-bluetooth-devices
     fn request_bluetooth_devices(&self,
                                  p: &Rc<Promise>,