Move hasEqualAttribute from Paint with adding some accessors

Paint#hasEqualAttributes is not a equal method in Paint.
TextLine depends on this method but making this public will make
developer confused. So, moving hasEqualAttributes to TextLine and
provide some accessors for shadow layer parameters.

For the TextPaint, unhide underlineColor and underlineThckness for
implementing equalAttributes in TextLine.

Bug: 112327179
Test: atest android.graphics.cts.PaintTest
Change-Id: I4565e18134856e31d26bd06bcddeb31ddbe7e093