[SuperTextField][SuperText] - SuperTextField golden failing after recent caret sizing fix

[matthew-carroll]

Recently we hacked a fix for the caret size due to a bug in Flutter when the caret sits at the end of text, after a space.

That hack generally seemed fine, but it apparently broke a golden test for SuperTextField. The failure isn't in the pixels, but rather in the layout process.

Update the caret hack so that it doesn't violate the layout assertion that was triggered in that test.