Add the sqlite3_vtab_collation() function, which allows an xBestIndex callback

Add the sqlite3_vtab_collation() function, which allows an xBestIndex callback
to determine the collation sequence that SQLite will use for a comparison. And
the SQLITE_DBCONFIG_FULL_EQP configuration option, which enhances the output
of "EXPLAIN QUERY PLAN" so that it includes statements run by triggers. And
the code for the sqlite3_expert extension and command line application.

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