SQLITE_DBCONFIG_DEFENSIVE flag

[brodycj]

Extra defense that "prevents ordinary SQL statements from corrupting the database file" (https://www.sqlite.org/security.html), as a followup to SQLite 3.26.0 security update (#837).

Will be part of the upcoming major release (#773) due to the potential for this to be a breaking change.

ref: https://www.sqlite.org/c3ref/c_dbconfig_defensive.html#sqlitedbconfigdefensive

NOTE that this is a run-time setting used in sqlite3_db_config() and not a compile-time build option like I had originally thought.