Update TextRunShaper to be backward compatible

This CL includes followings
- Returns -1 if there is no override
- Instantiate the variation instance.
- Use the same instance for the same FakedFont.

Bug: 361260253
Test: atest CtsTextTestCases
Test: atest CtsWidgetTestCases
Test: atest CtsGraphicsTestCases
Flag: com.android.text.flags.typeface_redesign
Change-Id: I2ea2b1504cb0c9ec67a38c11da411eff6e618e4f