Extract HashMapStylePropertyMap from CustomPaintImage and into its own file. Also rename to HashMapStylePropertyMapReadOnly for clarity.
Pull request: https://github.com/WebKit/WebKit/pull/7042
Committed 257299@main (ca9cbcaf3406): <https://commits.webkit.org/257299@main> Reviewed commits have been landed. Closing PR #7042 and removing active labels.
<rdar://problem/102913314>