Fixes InputDecorator to work with textScaleFactor, fixes Material Design differences.

There were a number of differences with the Material Design spec, including
several different padding values and underline thickness.  This corrects
that so that the decorator is in line with the Material Design spec now.

Also, the decorator properly handles changes to the textScaleFactor, where
before it would not re-layout when needed, painting the cursor and
underline incorrectly.

The decorator also now properly animates helper, error, and hint text when
the textScaleFactor or input decoration properties change.

Helper text is now properly displayed in dense mode, as the spec shows.
Before this change, it was never displayed in dense mode.

Fixes #12485