The outline box styles previously didn't allow a custom drawable to be set. The box background was handled by TextInputLayout, which nulled out the EditText's background and drew the boxBackground directly to the canvas. That meant that a call to TextInputEditText#setBackground() would not actually do anything - it would result in the same outline text field.
In order to respect the background drawable, TextInputEditText's background is set to null in the style. Then, TextInputLayout programmatically sets the custom outline drawable if the background is already null. This avoids overwriting a drawable that may have already been set on the TextInputEditText.
This change does pretty much nothing to the filled box style; since the EditText's underline is still being used, the background of the EditText was never set to null for that style. This change should be a no-op for that style.
This move to using the EditText's background for the outline also improves the bounds of the outline text field and gets rid of the cutoff that was appearing at the top of the outline when TextInputLayout's hint was disabled and a hint was set on the EditText.
PiperOrigin-RevId: 230538561
