Better brush previews

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Issue 2, the brush thumbnails. They're pretty interesting, I would consider them clever design, but it's just not practical when you pile up 100 different brushes like I have, at that point you no longer differentiate between them with their current thumbnails. My point is, I want to be able to see the brush asset itself, not some arbitrary representation of how it would look like if it were applied in a W-esque scribble of sorts. Otherwise I have to swap between dozens of different nodes to find exactly what I need in my vast library of brushes.
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The issue names no files, tests, or entry points. Start by locating the brush thumbnail and brush asset preview implementation, then compare the current thumbnails with the requested asset-focused view. Done should mean users can distinguish brushes in a large library without opening each one.

Written by the indexing model from the issue text.