Fix perspective handling in SmallPathRenderer

We currently ignore perspective transforms and pretend the scale is 1.
This bypasses the subsequent min/max checks and can cause numerical
stability issues for very large transforms.

Use bounds mapping to approximate the scales for perspective.

Bug: chromium:505876830
Change-Id: Iccf284c391cefb19b27de449d3534794204a2392
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1242376
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>