Add xml serialization for repeating effects

Introduce new tags to the vibration.xsd scheme to support repeating effects which could include a preamble.

Bug: 347035918
Flag: android.os.vibrator.normalized_pwle_effects
Test: atest android.os.vibrator.persistence
Change-Id: I2e14fec3d0310f1eec9683bd9d887facae82143b