Fix post text preview showing raw markdown

[hjiangsu]

Pull Request Description

This PR resolves an issue where the text preview for a post was showing raw markdown. To fix this, I used the markdown package to parse the markdown into it's AST tree, and took the textContent from the generated nodes. This seems to work for the most part, but may not fully render proper spacing for certain markdown.

Additionally, I made the text preview colour slightly lighter so that it doesn't clash with the main post title!

Issue Being Fixed

Issue Number: #1220

Screenshots / Recordings

Before	After

Checklist

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

[micahmo]

This looks good!

Keep in mind we already have a technique to convert markdown to plaintext by passing it through HTML. So maybe we could consolidate techniques.

thunder/lib/notification/utils/local_notifications.dart

Lines 100 to 101 in 8c8ce53

	final String htmlComment = markdownToHtml(commentContent);
	final String plaintextComment = parse(parse(htmlComment).body?.text).documentElement?.text ?? commentContent;

Although in this case, the HTML is needed anyway for the rich text notification, so it doesn't hurt to perform both steps.

[hjiangsu]

Ahh right - I completely forgot about that. I can go ahead and see if using the HTML parser works better!

[hjiangsu]

I adjusted the code using the same technique as what you referenced earlier. It should be good now!

[micahmo]

LGTM. The other technique parsed twice, and used body for the first pass and documentElement for the second. To be honest I don't remember why that was needed, but if this looks good in your testing, we'll go with it!

[hjiangsu]

Ahh yeah weird... I didn't notice anything off when I tested it so it might be fine? I'll go ahead and merge this in and I'll monitor if anything looks off!