Update msal-browser SilentHandler.monitorIframeForHash to be purely timing-based

[jasonnutter]

This PR updates the polling in SilentHandler to be purely timing-based, similar to #1823.

Other changes:

• Renames SilentHandler method to monitorIframeForHash
• Renames PopupHandler method to monitorPopupForHash
• Removes urlNavigate from error message, as it contains PII (will be added back later in errorPii log statement).
• Adds tests for both methods.

[coveralls]

Coverage increased (+1.4%) to 80.834% when pulling fdf9609 on browser-monitoriframeforhash-monitorpopupforhash into d907a56 on dev.

[pkanher617]

1 question but otherwise looks good