feat(non linear font scaling): add FontScaleConverterFactory.isNonLinearFontScalingActive()

This helps us determine if we can skip certain calculations as a
performance optimization, for instance when calculating line height
proportionally.

Bug: 273326061
Test: atest frameworks/base/core/java/android/content/res/FontScaleConverterFactory.java

Change-Id: I364a978b457c9b7a7073b34fa8cc1f3abaeabbac