Editorial: In favor of "owned element" and "owning element", uses "ac…

…cessibility parent", "accessibility child" and "accessibility descendant" (w3c#2010)

Closes w3c#1150

As discussed in the F2F, "owned" elements refers to either descendant or the direct accessibility child. Also, using "owned" in this way is confusing, because it is not exactly the same as "aria-owns".

Co-authored-by: giacomo-petri <106394951+giacomo-petri@users.noreply.github.com>
Co-authored-by: Peter Krautzberger <p.krautzberger@gmail.com>
Co-authored-by: James Craig <cookiecrook@users.noreply.github.com>