Function GetThemeTextExtent 

pub unsafe fn GetThemeTextExtent(
    htheme: HTHEME,
    hdc: HDC,
    ipartid: i32,
    istateid: i32,
    psztext: &[u16],
    dwtextflags: DRAW_TEXT_FORMAT,
    pboundingrect: Option<*const RECT>,
) -> Result<RECT>