Doc: Renamed HTML file for "Qt Multimedia on Windows" page.
Doc: Renamed HTML file for "Qt Multimedia on Windows" page.

Conflicts with the platform page for Windows in qt5/doc

Task-number: QTBUG-32580
Change-Id: Ibcf51c5dcd93ac388fa799644004c51aa88fe93d
Reviewed-by: Martin Smith <a8cc6484db2755056ccf1c457da8ca771f895dea@digia.com>

mer-qt/qtmultimedia,mer-qt/qtmultimedia,mer-qt/qtmultimedia,mer-qt/qtmultimedia,mer-qt/qtmultimedia