(Info-toc): Call Info-toc-nodes instead of Info-build-toc.

(Info-toc): Call Info-toc-nodes instead of Info-build-toc.
(Info-toc, Info-insert-toc): Increment nth's index to add PARENT
as the second element.
(Info-build-toc): Add PARENT element extracted from the Up pointer.
Don't print progress messages.
(Info-toc-nodes): New variable and function.
(Info-index-nodes): Optimize non-string file name case.
(Info-breadcrumbs-depth): Increment the default value from 3 to 4.
(Info-insert-breadcrumbs): Use the cached document structure instead
of visiting all ancestor nodes.  Remove the initial `>'.