Should the request reject or throw error if users denies changing network?

**Describe the bug**
`window.ethereum.on('chainChanged')` returns the same if users accepts or cancels

**Steps to reproduce (REQUIRED)**
Click, cancel when prompted to change network (see video)
https://user-images.githubusercontent.com/85146/131553143-db709d8a-9f80-443d-85c3-2586f96bd8aa.mov

**Expected behavior**
A clear description of what you expected to happen.

**Screenshots**

**Browser details (please complete the following information):**
- OS: [e.g. OS X]

- Browser: [e.g. Chrome Version ]
- MetaMask Version: [e.g. 5.0.2]

Reproduce the network-change flow by cancelling the prompt as described and inspect the handling of `window.ethereum.on('chainChanged')`. Determine the expected behavior for a cancelled network change—rejection or an error—and define completion around making the observed result distinguishable from acceptance.

Written by the indexing model from the issue text.