The current layout gave too little space for the full "Search" string inside
the button.
Fix this by making sure radio-buttons have their text center aligned by default
in pop-ups too, like they do anywhere else.
This does affect a few other cases, e.g. the "RGB"/"HSV"/"Hex" radio-toggles
for color pickers. But this should be fine, I don't think they were ever
intentionally using left-aligned text (while similar buttons outside of pop-ups
didn't).
7ee518cf70