PDF metadata uses non-standard `&` to separate authors (if `\and` was used in `latex_documents`)

Here is the relevant code: https://github.com/sphinx-doc/sphinx/blob/364f54cb5597bc6e5b619742492b4cae3067012f/sphinx/texinputs/sphinxmanual.cls#L44-L48

However, Adobe Pro apparently uses ; to separate author names. And it looks as if it also parses ,. I don't have access to such software so I can not check and my information is second-hand.

Some time recently, LaTeX package hyperref modified the behavior of its option pdfusetitle to recognize \and keyword in \author{....} input and to transform it into ; . See here.

Sphinx behavior perhaps is not quite a bug, the problem is at the time I introduced the & I has searched for some official clear guidelines on PDF author data, in case of multiple authors, and failed to find one.

I propose to adopt the ; separator.

Suggestions welcome! If no one opposes I wlll do the change in time for 2.3.0 2.4.0

Relates: #6875