Add scale factor fields to HapticGenerator AIDL

Add support for haptic scale factors introduced to the HapticScale
parcelable defined at HapticGenerator.aidl. These fields are used by the
platform to scale the haptic channel data before it's sent to the vibrator
motor.

The fields have a default negative value which will be interpreted as
undefined by the scale function and ignored. The VibratorScale enum will
still be supported by the platform when the scale factors are undefined.

Fix: 356406324
Fix: 356406686
Flag: EXEMPT HAL interface change
Test: VtsHalHapticGeneratorTargetTest
Change-Id: I9da0f6f2573722089efadb78ff96fc265bdad164