[WEBUSB] Connection breaks

[fabianhugo]

Describe the bug

In certain situations the WEBUSB connection somewhat crashes and a download of the program is only possible after a new manual coupling action. The known situations currently are:

• saving project settings
• adding an extension to the program
• clicking the "add blocks" button when Jacdac modules are connected

These action have in common that they seem to do an internal reload of makecode in the background.
That the connection breaks can be seen by missing USB icon next to the download button, interestingly the tab still shows a WEBUSB connection.

To Reproduce

1. Go to makecode.calliope.cc, connect device, establish WEBUSB connection
   Do one of the following:
2. Click on project settings and save
3. Click on extension, add any extension
4. Add jacdac extension, connect jacdac module, click add
   Then:
   The WEBUSB connection of makecode is lost, while the WEBUSB connection of the browser inside the tab seems to be intact.

Expected behavior
WEBUSB should remain connected, pressing download should trigger a transfer of the program.