Return a list of locations documenting COMMAND.
The `info-file' property of COMMAND says which Info manual to search.
If COMMAND has no property, the variable `Info-file-list-for-emacs'
defines heuristics for which Info manual to try.
The locations are of the format used in `Info-history', i.e.
(FILENAME NODENAME BUFFERPOS), where BUFFERPOS is the line number
in the first element of the returned list (which is treated specially in
`Info-goto-emacs-command-node'), and 0 for the rest elements of a list.