This commit updates the `fetch` patch for zone.js. Currently, we're attaching an
`abort` event listener on the signal (when it's provided) and never removing it.
We should be good citizens and remove event listeners whenever objects need to be
properly collected. In Firefox, when saving a heap snapshot and running it through
`fxsnapshot`, querying `AbortSignal` will print a so-called "CaptureMap" with a list
of "lambdas," indicating that the signal is not garbage collected because of the event
listener lambda function.
PR Close#57882