Upstream recent changes from sanitizer API after main upstreaming

[noamr]

What is the issue with the HTML Standard?

Some recent changes to sanitizer API need to be upstreamed as a follow up.
Specifically WICG/sanitizer-api#385 was merged in after the upstreaming was already advanced.

[noamr]

cc @otherdaniel @evilpie

[evilpie]

We also have WICG/sanitizer-api#396 which should probably just be a new PR to HTML now.