bpo-42972: Track sqlite3 statement objects (GH-26475)

Allocate and track statement objects in pysqlite_statement_create.

By allocating and tracking creation of statement object in
pysqlite_statement_create(), the caller does not need to worry about GC
syncronization, and eliminates the possibility of getting a badly
created object. All related fault handling is moved to
pysqlite_statement_create().

Co-authored-by: Victor Stinner <vstinner@python.org>