Polyfills Throwing Uncaught Exceptions in Safari 11.1

### Description

2 Polyfills seem to be the cause of thousands of uncaught exceptions. These end up swamping our logs making it difficult to track other problems.

1. `TypeError: setTimeout is not a function` position-observer.js:116
2. `TypeError: undefined is not an object (evaluating 'Math.round')` intersection-observer.install.js:786

Both are quite shocking but also both point to ampproject source. As a publisher, we do not have control over the ad content and technology. Not sure which ad vendor is the culprit either.

Screenshot below.


links to sources:

https://raw.githubusercontent.com/ampproject/amphtml/2107240354000/ads/inabox/position-observer.js
https://cdn.ampproject.org/rtv/012107240354000/v0/amp-intersection-observer-polyfill-0.1.mjs

New Relic breakdown of errors chiefly related to this by platform (30 minute window):


### Reproduction Steps

go to https://www.accuradio.com from Safari 11.1
open console
click a channel image to play and launch banner
wait for errors, if no errors yet click genres in left nav to cycle ads (15 second lockout per cycle)

### Relevant Logs

_No response_

### Browser(s) Affected

Safari

### OS(s) Affected

Mac High Sierra but others as well.

### Device(s) Affected

_No response_

### AMP Version Affected

2107240354000