Replace Text link handling with LinkInteractionListener

[dfabulich]

Fixes #435

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  Example of intercepted Markdown link text skipapp-showcase#105

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Cursor did this; I tested it in the Showcase Lite app.

[dfabulich]

This PR will conflict with #434.

Fun fact! I generated #434 and skiptools/skip-foundation#122 basically by accident, trying to fix #435.

Cursor said "I know, why don't I just implement AttributedString for real?!" and then went ahead and just did it.

I looked at the resulting code and said… "Uh, this… this seems pretty good, but it's way overkill for what I needed to do. But… I can't just throw all this away, can I?!?" So I filed the other PRs in the hopes that I (or someone) actually fixes this at some point.