A selectedcontent element's option clones must not be options of its select - #77273

8d4efe2

A selectedcontent element's option clones must not be options of its select
https://bugs.webkit.org/show_bug.cgi?id=327828
rdar://190223089

Reviewed by NOBODY (OOPS!).

When a selected option's subtree contains a nested option, cloning it into a
selectedcontent element placed a cloned option into the select's list of
options. With a selected nested option this looped forever (each clone became
the selected option, re-running the update); without one, select.options still
wrongly included the clone.

A selectedcontent element only ever holds clones, on both the single and the
multiple selection paths, so treat it as such unconditionally.

Test: imported/w3c/web-platform-tests/html/semantics/forms/the-select-element/customizable-select/selectedcontent-cloned-option-is-not-an-option.tentative.html

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