[WPT] Move green-100x100 images

Move the images from the css-masking directory to the general
/images directory as they will shortly be used by a host
of HTML-in-Canvas tests.

Bug: 507356242
Change-Id: I5916994dd4796410e03ee7fa61652407439894ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7851076
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Auto-Submit: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1631808}
NOKEYCHECK=True
GitOrigin-RevId: 23b7263ae16fd94391c47d38e14ef00a6062abf3