Fix for ticket [b2fa5424e6fcb15]: Better define the format of the sqlite_stat4

Fix for ticket [b2fa5424e6fcb15]: Better define the format of the sqlite_stat4
file for WITHOUT ROWID tables and make sure the ANALYZE command generates a
file in the appropriate format.  Use the sqlite_stat4 data to enable the use
of WHERE terms that cover all indexed columns plus some prefix of columns
in the primary key.

FossilOrigin-Name: bc2de8095fa9c385db0adf22ca55b0298a33c284