Change signature of GrAtlasGlyphCache::getProxies

Split out of https://skia-review.googlesource.com/c/skia/+/108001 (Fission GrAtlasGlyphCache in two)

TBR=bsalomon@google.com
Change-Id: I573730fdeddf178915eb5f5b8cf59a3ab29e0654
Reviewed-on: https://skia-review.googlesource.com/108441
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
6 files changed