SurfaceFlinger: Allows Surfaces to outlive their parents.

Currently the only strong reference to a Layer is held by
their parent or the containing layer stack. This has a few
undesirable implications. Firstly, it means that we can not
create a SurfaceControl with a null parent. For example, a
media decoding library may wish to offer an unparented SurfaceControl
representing the decoding Surface, and allow the consumer to parent
it between various SurfaceControls as they wish. Secondly it requires
lifetime coordination between various levels of the hierarchy, when adding
a child you have to be careful to observe the lifetime of the parent because
your BufferQueue may become suddenly abandoned at any point. In this change
we switch to a reference counted model, such that the Layer remains valid
as long as there is a handle to it. We also end the behavior of passing on
BufferQueue abandon to children. Layers are only abandoned/disposed when
an explicit call to remove is made, or the last reference is dropped.

Bug: 62536731
Bug: 111373437
Bug: 111297488
Test: Transaction_test.cpp
Change-Id: I04cbc2368a1049b8ebd8913673ed4bfe05a26280