Add texture-specific flags for External & Rectangle textures

For DDLs, Ganesh needs to know about External & Rectangle textures prior to instantiation (or PromiseImage fulfillment). These new flags allow the client to provide this information when the lazyProxy is created.

The new texture flags work analogously to the render target flags:
   GrSurface and GrSurfaceProxy get a new set of accessors for the new flags
   The new flags are set appropriately on a GrGLTexture when it is created
   For wrapped texture proxies the flags are just copied off of the GrSurface
   For lazy-proxies/promise-images the flags are computed up front and passed to the proxy
   The GrSurfaceProxy/GrSurface flags equivalence is verified in GrSurfaceProxy::assign

Change-Id: Ia8e1998aa0a36ce4481bfd9e56be21f990e83148
Reviewed-on: https://skia-review.googlesource.com/114985
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed