Improve link handling in posts/comments

[micahmo]

Pull Request Description

This PR improves the functionality of links within posts and comments.

1. There is now an InkWell effect around links to make it more clear that you're tapping on an interactable element.
2. There is now a long-press menu with...
   1. A link preview.
   2. The full URL.
   3. The ability to open, copy, or share.

There are a few caveats with this implementation.

1. Elements that are formatted by markdown and then surrounded by a link lose their additional markdown formatting. This is probably fixable, but with a lot of work.
2. Even more strangely, as soon as we provide our own builder for the a element, all text surrounding a link on the same line becomes tappable. To handle this, I removed our onTapLink handler, which does solve the problem, but it also means that the text is not tappable in any capacity. That causes a small issue when viewing a CommentReference because it means you can't tap on the text surrounding a link to navigate to the comment. You have to tap on another line or outside the body.

Feel free to experiment to see what I mean by these issues, and if they're dealbreakers, I can keep working on it.

I'm going to leave this as a draft for now until I've had a chance to daily drive it.

Issue Being Fixed

Issue Number: #309, #709

Screenshots / Recordings

qemu-system-x86_64_xfbhehNZpv.mp4

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[micahmo]

I've been daily driving this and it seems to be working very well, so I'll mark this ready for review!

[hjiangsu]

LGTM!

[hjiangsu]

Awesome, in that case, I'll go ahead and merge it in so that we can slot it into the nightly build