Minimap "block" mode

[PHLAK]

First off, thank you so much for adding minimap support! This is one of the few major features I've been missing in Zed.

That being said, as it is, since it's so small, the minimap text just looks blurry. It would be nice to have a "block" rendering mode where, instead of rendering the text itself in the minimap, it showed as a "block" representation of the text instead.

[aurexav]

As described in #5308 (comment).

Would love to see this.