Text Fragments: Add tests for search-invisible content inside a text directive parameter.
Existing tests only cover search-invisible content in between text directive tokens (eg. between prefix- and start),
but not inside of a text directive parameter.
Since this is a use case that happens rather frequently (e.g. an image inside a text node), there should be tests for this.
Differential Revision: https://phabricator.services.mozilla.com/D216688
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1908118
gecko-commit: 56d722e540c78c0703711c3d67708bdac63ded9e
gecko-reviewers: peterv, dom-core