[bazel] Add option for SkSVGCanvas (and expat third_party DEP)

Our SVG code depends on our XML code which depends on expat.

See also cl/457481999

Change-Id: I83b61f5d73570d0aa7e851a01ccd019b4b1019e4
Bug: skia:12541
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/553376
Reviewed-by: Florin Malita <fmalita@google.com>
10 files changed