Update the impl of wghtOverride and italOverride

The wghtOverride and italOverride are not used in the redesigned
variation settings. These values are stored in the variation
settings instead. To keep the existing behavior, find the value
from variation settings and return it.

Bug: 361260253
Test: minikin_tests
Flag: com.android.text.flags.typeface_redesign

Change-Id: I2fc987ea3db14cf62d5aa807f428d19f3892cbfa