part 4: Add WPTs to test modifications to a SVG image element's href and xlink:href attributes.
This patch adds each new test as a modified-copy (with 'hg cp' + edits) of the
correspondingly-numbered "image-remove-href-*" test.
Differential Revision: https://phabricator.services.mozilla.com/D217175
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1908991
gecko-commit: 89d7e04661609392c93be396d87992627b6db3f6
gecko-reviewers: longsonr