Redesign program key construction

This does two things:
1) Moves responsibility for bit-packing portions of the key into the key
   itself. A new GrKeyBuilder type manages adding bits, with asserts to
   ensure a value always fits in the requested number. In theory this
   will let us generate smaller keys overall, at the expense of slightly
   more complex code during construction.
2) Adds a string label parameter for key methods that fold in data. For
   new methods, the label is required. To ease migration, the old add32
   does not require a label (yet). This will let us generate detailed,
   human readable keys, either based on SK_DEBUG, or a runtime option
   (if we're comfortable paying the cost).

Bug: skia:11372
Change-Id: Ib0f941551e0dbadabbd2a7de912b00e9e766b166
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377876
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
18 files changed