xShadowName method is added to the sqlite3_module object and is used
to identify potential shadow tables. The SQLITE_PREPARE_SHADOW argument
to sqlite3_prepare_v3() is defined. It is designed to permit writing to
shadow tables, but is currently an unused placeholder.
FossilOrigin-Name: 31942b3dd3f66eb0d9977bf1cadc2f2d7be7967cce2b55784be0b939dfef1985
for additional test cases for the optimization that avoids updating indexes
on expressions when none of the columns changed by the UPDATE are in the
expression.
FossilOrigin-Name: 2404304cc15eaeee2744cf3c8f9cac0a544631c4f1060c5a17a78b43ca86edf0