Add a remote control mechanism for window containers

This adds a "IWindowContainer" interface which is an opaque
handle to a window-container in WM. It has very minimal
functionality and is intended to be used mostly as an
identifier.

Along with this handle, there is a WindowContainerTransaction
which can collect a set of container + configuration changess
and apply them all together. This will be used for remote
rotation control and other batched operations in the future.

Bug: 124011688
Test: Added some wm/core tests.
Change-Id: I691e7c11cd8c30f1a24fd64c6018a18933047847