ohos: Extract makeWebComponentAttributes() member function

Move the inline Web component attribute object out of
createEmbeddedWebComponent() into a new makeWebComponentAttributes()
member function, and pass the prebuilt object to
createEmbeddedWebComponent() instead.

This is a pure refactoring with no functional change. It prepares
for applying QWebViewSettings to the Web component in a following
commit.

Task-number: QTBUG-146838
Pick-to: 6.12
Change-Id: Ie5c9adf61b9085930a0019c480768fb86df412a2
Reviewed-by: Zbigniew Chyla <zbigniew.chyla@qt.io>
Reviewed-by: Liang Qi <liang.qi@qt.io>