Fix ExternalVibrationUtilsTest after fix flag enabled

Add flag controls to tests that allowed vibration scale to output values
outside the PCM bounds of [-1,1], so the behaviour is preserved only
when the fix flag is disabled.

Fix: 432785244
Test: ExternalVibrationUtilsTest
Flag: android.os.vibrator.vibration_scale_bounds_fix_enabled
Change-Id: I93ab663198e6339239d5de6ea16a438ab6473eda