Export libcore aconfig flags to frameworks-minus-apex bootclasspath

The DateIntervalFormatTest.testIsLibcoreVFlagEnabled() doesn't pass in AOSP today, even though `printflags` shows `core_libraries/com.android.libcore.v_apis: READ_ONLY + ENABLED (/apex/com.android.art)`. So try to submit it in internal main instead.

Bug: 349108429
Test: atest FrameworksCoreTests:android.text.format.DateIntervalFormatTest
Flag: EXEMPT Add exported flag lib
Change-Id: I6244a615ae3d1c82bcf367c6e06994741c0553bb