Add the index_xinfo pragma which gives information about the fields that

Add the index_xinfo pragma which gives information about the fields that
reference the table PRIMARY KEY in addition to the index key fields.
Add extra columns "desc", "coll", and "key" to the index_info and index_xinfo
pragmas.  Add the "origin" and "partial" columns to the index_list pragma.

FossilOrigin-Name: 2743846cdba572f616f56d310633703b8b50959e