Move SkPixelXorXfermode.h to include/client/android
This intended to make clients aware that the SkPixelXorXfermode is Android-specific
This needs to land after the Chromium CL https://codereview.chromium.org/
1647953006/ (Add include/client/android to skia .gn & .gypi files)
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=
1645093002
Committed: https://skia.googlesource.com/skia/+/
aa9cb62901075e9d2858353cb041e5e6d4719614
Review URL: https://codereview.chromium.org/
1645093002