Add a RenderBuffer object to store stencil buffers.

Bug #7146141

This change is needed to add a render buffer cache to avoid
creating and destroying stencil buffers on every frame.

This change also allows the renderer to use a 1 bit or 4 bit
stencil buffer whenever possible.

Finally this change fixes a bug introduced by a previous CL
which causes the stencil buffer to not be updated in certain
conditions. The fix relies on a new optional parameter in
drawColorRects() that can be used to avoid performing a
quickReject on rectangles generated by the clip region.

Change-Id: I2f55a8e807009887b276a83cde9f53fd5c01199f