Add SkSVGCanvas api Fuzzer

When manipulating svg file, the implementation of SkSVGCanvas will be used instead of the 
implementation of SkCanvas, so the api are tested against SkSVGCanvas. In addition, there are 
more api need to be covered in the function fuzz_canvas. As a result, the main changes are to 
add new DEF_FUZZ for SkSVGCanvas and to modify fuzz_canvas to increase the coverages of api.

Change-Id: Iaf6114bb0e2929c73549ff398c3db5592e736ea2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/298977
Commit-Queue: Zepeng Hu <zepenghu@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
3 files changed