[HiC] Initial support for privacy preserving painting

Add the paint flag for privacy preserving painting and use it
to not draw "disallowed access" images (a concept that already
exists for canvas tainting and image-orientation). This covers
HTML image elements and SVG image elements.

Still to do is SVG foreign object content testing, and images
used in filters. Plus all the non-image content to disallow
including video and iframes.

Bug: 426580072
Change-Id: I6c8c53f33d397452fc7c207ce143401e09237877
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6704465
Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1483720}