React Native fetch memory leak in 0.59.0-rc.3 and earlier versions

This is a pretty severe memory leak.

• I've confirmed that this is happening in 0.57.8, 0.58.6, and 0.59.0-rc.3.
• I've tried this with both node-fetch and whatwg-fetch and it happens using both libraries.
• It is not isolated to response.blob(). It affects all types of responses.
• It happens with both Release and Debug.
• I've only tried this on iOS.

This is possibly related to, but different from:

• facebook/react-native#20352
• facebook/react-native#19248
• facebook/react-native#19333
• expo/expo#2402