feat(NotificationBlock): UI to show blocked posts

[marcustyphoon]

Description

Simplified version of #1071, this time without saving the user's blog UUIDs into storage (per precedent set in #450).

This implements a UI for NotificationBlock's preference pane similar to PostBlock's, including additions in #719. That is, it displays a list of posts that one has blocked notifications for, including the ability to click to navigate to the posts in question (so that, for example, one can migrate to the native "notification muting" feature instead).

This requires opening a post purely based on its post id, something which the Tumblr API isn't able to do. Therefore, this assumes the post is probably on one of the currently logged in user's blogs, and simply checks each blog the user has access to in descending order of post count for the post in question.

If the user uses container tabs, they'll have to right click the link and open it in the correct, logged-in container tab for this to work. The only way I could think of to do this was to make the link real and include a query parameter in it, which is a bit clunky since it persists once you close the blog view modal. This is therefore of last resort.

Testing steps

todo: document tests

[marcustyphoon]

• make link color reasonable in firefox dark mode