Button Block: Refactor to avoid cropping the URL input field

[kjellr]

When a button has short text, the URL input field is cropped initially, cutting off part of its placeholder text:

This should be adjusted so that the text isn't cut off, but so that it will (ideally) still fit in areas where there isn't much room.

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Originally noted in #17063, related to updates made in #16873.

[talldan]

A couple of other issues that might also have resulted from #16873.

The movers are incorrectly sized when a left/right alignment is set on the button block:

Block warnings aren't full width for the button block:

[skorasaurus]

I came across this while debugging another button issue; this appears to now be fixed; I'm unable to reproduce this, regardless what alignment is used.

Below is what appears even while emulating a small moto4 (width 360px) in chrome

[kjellr]

It is! The URL field has moved back into a popover, so this is no longer an issue. Thanks for the nudge!