Refine haptics and snap zones for magnetic split divider

- Refactors MagneticDividerUtils to utilize more advanced Kotlin and match the MotionValue API better.
- Haptic now only plays on attach, not detach.
- No longer plays a snap or haptic at the screen edge.
- Widens the snap zone to 56dp on each side.
- Softens the magnetic spring to 850/0.95.

Bug: 383631946
Flag: com.android.wm.shell.enable_magnetic_split_divider
Test: MagneticDividerUtilsTests
Change-Id: I0f34f5101b6a875b0c5f051fb121c029685e9c71