Convert sanitized HTML into Markdown

[alicerunsonfedora]

• I know that I'm requesting a feature for Codename Starlight (SwiftUI) and not for Hyperspace Desktop (JS).

Previously, we aimed to try rendering the sanitized HTML content from a status with #6. However, with the new improvements in SwiftUI, we should be able to convert this into Markdown for SwiftUI to render on its own.

Tasks

• Convert emojicodes (:thumbsup:) into their corresponding emojis (👍🏻)
• Parse anchor tags (<a>) into proper Markdown links that the deep linker can use
• Strip away basic HTML attributes and replace them with Markdown equivalents (ex.: <b> to **, <I> to _)
• Add cards for extra information that a status provides (see also: Add a full-fledged media viewer + support for more media types #11)

Note: This issue supersedes #6.