Move code writing pycairo images to a global function
This will allow follow-up CLs to reuse this code for generating other
images using pycairo.
Bug: 364549423
Change-Id: I340bea1153a82145f06c859e44fc4828d9a38d8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5891403
Reviewed-by: Andres Ricardo Perez andresrperez@chromium.org
Commit-Queue: Jean-Philippe Gravel jpgravel@chromium.org
Cr-Commit-Position: refs/heads/main@{#1361438}