5064532: GridLayout with initial "stretchy" row and "gone" view in last row doesn't stretch properly
Also:
. Infer stretchibility from whether or not gravity is defined.
. Make algorithms for handling flexibility within cell groups consistent
with those acting between cells groups (via constraint system).
. Hide and deprecate methods taking flexibility argument.
. Hide and deprecate CAN_STRETCH constant.
Both deprecated features will be removed after references are removed from platform.
Change-Id: Iabf2bf19f35cf30b8ec49c99b49a0550fd495125
5125e21bc0