Add link annotation support to SkSVGDevice.

This CL implements |SkSVGDevice::drawAnnotation|, overridden from
|SKBaseDevice|.  |drawAnnotation| supports annotating rectangular areas
of a Skia device.  Previous to this change, annotations are being used
in |SkPDFDevice| to include hyperlinked rectangular areas in .pdf
documents.  This CL implements the SVG equivalent of this PDF feature.

BUG=skia:7581

Docs-Preview: https://skia.org/?cl=104680
Change-Id: I92ae01ceb7ae10cd2010bebab2a58dcfe48ef253
Reviewed-on: https://skia-review.googlesource.com/104680
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
5 files changed