In extensions rtree, fts3 and fts5, ensure that when dynamic buffers are bound

In extensions rtree, fts3 and fts5, ensure that when dynamic buffers are bound
to persistent SQL statements using SQLITE_STATIC, the binding is replaced with
an SQL NULL before the buffer is freed. Otherwise, a user may obtain a pointer
to the persistent statement using sqlite3_next_stmt() and attempt to access
the freed buffer using sqlite3_expanded_sql() or similar.

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