Inconsistent "Reset" controls in the block settings sidebar.

[kjellr]

The text size and color controls in the block sidebar have buttons/links to "reset" to the default settings, but their treatment and labels are inconsistent. You can see this most evidently in the Paragraph block sidebar:

I'd suggest we change all to use text links, and go with "Reset", since that seems like a clear label for both. I'd also suggest that these links don't need to appear if settings haven't been changed yet.

[ZebulanStanphill]

I'd also suggest that these links don't need to appear if settings haven't been changed yet.

Alternatively, the buttons could be visible, but disabled when there is nothing to reset.

[mtias]

Tracking in #27331.