Handle dates with relative time when streaming blame page

When Add streaming to Blame page full view (!110208 - merged) is merged we should also consider handling relative dates when streaming.

With streaming enabled only the dates that came before the streaming are updated. We should fix that and handle all the dates that come with a streamed HTML. We could achieve that by leveraging MutationObserver and IntersectionObserver in conjunction wrapped within a throttle to avoid blocking main thread unless the date has appeared in the viewport.

Dates visual comparison

Relative date	Absolute date