[BACKPORT] Fix -Wstring-concatenation warnings in clang 12 am: 94ed3ab33d am: b583dd232f am: 537f5dea6f

Original change: https://android-review.googlesource.com/c/platform/external/skqp/+/1924038

Change-Id: If4859dfc68d109b699f8cfc42ec2e5b0c7ec301f