[Webapp] API Client and API Explorer Not Timing Out

[andrewdimmer]

Describe the bug
When a request to a function times out, the client remains in the "Pending response..." state until the next request is made, and presumably,

To Reproduce
Steps to reproduce the behavior:

1. On functions, create (or find :| ) and endpoint with no send statement
2. Start the emulators using firebase emulators:start
3. From the hosting emulator (localhost:5000) or the React app debugger (localhost:3000 started from npm run start in the webapp directory), call that endpoint from the API Explorer
4. Wait until the function times out in the emulator logs. You'll see that the API Explorer does not do the same.

Expected behavior
Shortly after the function times out, the API Client connection should timeout as well, and that timeout should be broadcast to the API Explorer.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Windows 10 Home (2004)
• Browser: Chrome 88.0.4324.190 (Official Build) (64-bit)
• Version: Node 14.16.0