Toggle to filter all media that lacks media descriptions

[dariusk]

Pitch

Add a toggle to the Home timeline that filters out posts that have media but lack media descriptions (image descriptions, audio descriptions, etc).

Alternately, a toggle in user preferences, probably in the filters section, that removes the above posts globally instead of just in the one timeline.

Idea from: https://dragonscave.space/@talon/109394762838024173

Motivation

Users who rely on media descriptions, for example screen reader users, should be able to have access to a feed that is free of content that is not readable for them.

[lawremipsum]

I think this makes sense in the filters section because it's pretty likely if someone wants it for one timeline it wants them everywhere. Though it would be more flexible to allow the toggle to use the same multiselect option for filter contexts as any other filter.

I realize that's more work and the flexibility may not be necessary—I'm mostly thinking about a user that wants them generally filtered but might want to let DMs go unfiltered?