SurfaceFlinger: Expose construction of container layers.

WindowManager will imminently use them as Buffer-less Surfaces for catching
input. They can also be used for the existing hierarchy layers that the WM
adds to solely act as containers.

Bug: 111440400
Test: None
Change-Id: Ic7d9234d7fd8be74b77dfbc3daa6ca0e52f25768
Merged-In: Ic7d9234d7fd8be74b77dfbc3daa6ca0e52f25768