[flexiglass] Implement stack scroll on remote input activation in Shade

When remote input is started, we pipe the target bottom bound of the remote input row after its expansion animation to flexiglass, where we diff that value with the target top bound of the IME after its expansion animation. We then artificially add the IME height to the stack content height, and scroll it by the diff so that the remote input row isn't overlapped by the IME.

Bug: 359876385
Test: manually verified stack scrolls above IME when remote input starts
Test: manually verified stack scrolls above IME when a second remote input is started while another is already active
Test: manually verified stack scrolls above IME even when there is no space below the remote input row, and then scrolls back down when IME is dismissed
Test: manually verified remote input in HUN is unaffected
Flag: com.android.systemui.scene_container
Change-Id: Ibe85ae9f6e10502fcf986b3a0056f57716a2cbb5