Accept float values in Vibrator setAmplitude

This is a first step towards unifying the waveform APIs to prepare for
the PWLE composition. The IVibrator.aidl already supports float
amplitude values, so this also exposes the complete supported amplitude
range.

Bug: 167947076
Test: atest libvibratorservice_test
Change-Id: Icd60cfa51807846de064052ab38a06ae21772755