[graphite] Move the bicubic padding constant out of GrBicubicEffect

This removes another Ganesh-specific usage in code that will be shared in the large image tiling API (i.e., in draw_tiled_bitmap).

Bug: b/267656937
Change-Id: Id730b51d0a40b0eca8e7d7e67e2fe9feb071a0a3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/702337
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
4 files changed