Several screen reader improvements
I got around to trying Tokodon in a screen reader again, and boy do we need some work! Here's some improvements:
- Remove the "Show Alt" button from the tab button order, because it's only for mouse/sighted users.
- Improve sensitive media handling, aka don't read out NSFW alt text.
- Announce standalone tag buttons as "tag buttons".
- Announce the content notice to the screen reader.
- Announce the interaction count for buttons (if enabled) to the screen reader.
- Announce the post content to the screen reader, and strip out the HTML so it doesn't take ages to listen to a post.