- Update Background section to take into account different browser's behavior
- Update Other Alternatives Considered section to explain in better detailed why Chrome is not supportive of declarative urls

Proposal has been updated so it can fit every browsers model by adding a url option parameter, with this requirements:
- In Chrome, we can require tab ID or document ID, but not `url`.
- In Safari, they can require `url`, but not `tabId` or `documentId`.
- If both are provided, they'll both be respected.

It also adds a method to remove the request and specifies when the methods resolve

- Change name to `permissions.addSiteAccessRequest()`
- Fix API comments

Co-authored-by: Rob Wu <[email protected]>