A brave new world for window insets (1/n)

This CL starts a journey to discover a brave new inset world. The
path to get us there may be rocky, but it's going to be rocky.

One of the main pledges of the new API is that an app can retrieve
what is causing a certain inset easily. For that, we need to
dispatch metadata who is causing what inset, such that we can query
it from the client side.

Furthermore, the client will be able to manipulate insets directly,
but also listen to animation changes. We don't want to go through
window manager for that, thus, there needs to be a local codepath
from (global window state -> WindowInsets).

Because we have these two requirements, we dispatch the relevant
global window state for insets, represented by InsetsState, and
dispatch it to the client. On the client side we take the frame
and the InsetsState and generate WindowInsets out of it.

Bug: 118118435
Test: InsetsSourceTest, InsetsStateTest, InsetsSourceProviderTest,
InsetsStateControllerTest
Change-Id: I2bfe9dda376512916261823fc2ee35cbedeb6731