Recents onboarding fixes

- Allow onboarding to be disabled for tests
  - If isDemoUser(), onboarding is disabled by default
  - Can force disabled via "adb shell setprop
    persist.quickstep.onboarding.enabled false"
- Fix crash when hiding onboarding while it's animating by
  canceling the animation (so it doesn't remove the view)

Test: used adb shell setprop and verified onboarding no longer
shows up; dismissed onboarding while animating and verfied
no crash occurs

Bug: 73549472
Bug: 73345650
Change-Id: I03a58ac8b0f2bb42090c0d02bd196f55dc115ec2