Implement fallback line spacing for BoringLayout

The fallback line spacing is a feature of extending the line height
when the fallback font has taller glyph. This was implemented to
StaticLayout in Android P but not yet implemented in BoringLayout.

This CL enables this feature to the BoringLayout as well.

Not to break existing apps, change this behavior only if the
targetSdk version is T or later.

Bug: 210923482
Test: atest FallbackLineSpacingTest BoringLayoutFallbackLineSpacingTest
Test: atest CtsGraphicsTestCases
Test: atest CtsTextTestCases
Change-Id: I6214d52cde25a044bc6e246d2118e35d3a243c9d