Address comments from API council for Font/FontFamily

- Change Font/FontFamily final
- Introduce equals/hashCode to Font class
-- Add equals and hashCode to FontVariationAxis as well
- Rename FontFamily.getFontCount to FontFamily.getSize
- Change Font ctor not to throw IOException and throw that in build()
  instead.

Bug: 112303038
Test: atest CtsWidgetTestCases:EditTextTest
    CtsWidgetTestCases:TextViewFadingEdgeTest
    FrameworksCoreTests:TextViewFallbackLineSpacingTest
    FrameworksCoreTests:TextViewTest FrameworksCoreTests:TypefaceTest
    CtsGraphicsTestCases:TypefaceTest CtsWidgetTestCases:TextViewTest
    CtsTextTestCases FrameworksCoreTests:android.text
    CtsWidgetTestCases:TextViewPrecomputedTextTest
    CtsGraphicsTestCases:android.graphics.fonts

Change-Id: I079c99cfd579d07b6f3643e41415e58dc8b26492