Detach op memory pool from recording context

This changes GrOpMemoryPool to no longer extend SkRefCnt, and all usages
either are std::unique_ptr for owners, or GrOpMemoryPool* when ownership
is held somewhere else. The culmination of this is that DDLs explicitly
detach the memory pool from the recording context instead of the GrOpsTask
maintaining a strong ref that preserved the memory somewhat sneakily.

Change-Id: I33e2caebea70cebe8fd7681207c631feeaf2c703
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/259424
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
13 files changed