Remaining CSS-UI Bugs on mandatory requirements with less than 2 implementations

* cursor: auto
https://bugs.webkit.org/show_bug.cgi?id=173909
https://bugs.webkit.org/show_bug.cgi?id=173910
https://bugzilla.mozilla.org/show_bug.cgi?id=1376718
https://bugs.chromium.org/p/chromium/issues/detail?id=737452


* non-fixed-sized svg as a cursor
https://bugs.webkit.org/show_bug.cgi?id=173911
https://bugzilla.mozilla.org/show_bug.cgi?id=1376716
https://bugs.chromium.org/p/chromium/issues/detail?id=737459