Roll third_party/wuffs to version 0.3.0-alpha.21
Roll third_party/wuffs to version 0.3.0-alpha.21

Update Wuffs to match the version currently used by Chromium
(updated in http://crrev.com/c/2731168)

Change-Id: If3f1ccad6a9ff6202391ee79a9b4d3b413a4cc25
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/386756
Auto-Submit: Leon Scroggins <995cad867ca30d6399abe011583a53547c8afea1@google.com>
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@google.com>
Commit-Queue: Leon Scroggins <995cad867ca30d6399abe011583a53547c8afea1@google.com>

aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia