Tweak GrSmallPathAtlasMgr's cached path discovery methods

In an ideal world we wouldn't keep re-allocating the memory for the keys

Change-Id: I3b7954e131d483166d0bf0ce95510365869b134c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309123
Reviewed-by: Adlai Holler <adlai@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
5 files changed