LayoutLib: Change nullity annotations.

Switch from using tools nullity annotations (com.android.annotations)
to android framework annotations (android.annotation).

A new sdk-common prebuilt is required for LayoutLib tests. The new
sdk-common requires an updated tools-common. The updated tools-common
doesn't have nullity annotations. So, instead of adding the annotation
dependency, just reuse the platform ones. This also paves the way to
include other platform annotations like IdRes etc.

Change-Id: I87b8f767d3681d914abe7d1329e26a87f49f50a7