Implement animateNavBarLongPress for stashed taskbar.

I think ideally we would tie this into the taskbar's outline
provider, but it seemed more complicated to deal with existing
stashing animations.

Instead I've just animated the stashed taskbar scale to 0.85 or
1.18, depending on the SHRINK_NAV_HANDLE_ON_PRESS flag. These
are based on the existing navbar shrink/expand animations.

Demo (the flickering doesn't happen on-device):
https://drive.google.com/file/d/1CWCPRsuD3kjtOUbwXspkQ_ZJ6Ln7FnUo/view?usp=sharing&resourcekey=0-kJjfgnuEca1de4u8mbHrig

Bug: 308693847
Test: Manual
Flag: LEGACY SHRINK_NAV_HANDLE_ON_PRESS DISABLED
Flag: LEGACY ANIMATE_LPNH DISABLED
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:3a7a76f88e51453cc4b70fa68aef2724cccc02c6)
Merged-In: I6ecbc849ac1c066a4c018325f0237a61641d99aa
Change-Id: I6ecbc849ac1c066a4c018325f0237a61641d99aa