Make program key descriptions available in release builds

Whenever we need the description (as we're putting something in the
persistent cache), go back and re-compute the key to get the
description. This pattern means that we pay a (very) small overhead for
virtual dispatch in the common case, and only pay for the expensive
string work when we're already doing expensive work (compiling).

Bug: skia:11372
Change-Id: I3d4dc19f2d8883f8117f5f6489fc852cf9503eb3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/380359
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
13 files changed