[DocsUI Peek] Fix MetadataBottomSheetControllerTest

When the flag is disabled, the feature is optimized out of the APK,
leading to NoClassDefFoundError test failures. Hide test behind peek
flag.

Bug: 416377408
Bug: 427552739
Flag: com.android.documentsui.flags.use_material3
Flag: com.android.documentsui.flags.use_peek_preview_ro
Test: MetadataBottomSheetControllerTest
Change-Id: I5d039e9ff65027dc20eec45d574bdf46d07c1052