Gracefully degrade for SQLite JSON receiving direct numeric value

Gracefully degrade for SQLite JSON receiving direct numeric value

Fixed issue to workaround SQLite's behavior of assigning "numeric" affinity
to JSON datatypes, first described at :ref:`change_3850`, which returns
scalar numeric JSON values as a number and not as a string that can be JSON
deserialized.  The SQLite-specific JSON deserializer now gracefully
degrades for this case as an exception and bypasses deserialization for
single numeric values, as from a JSON perspective they are already
deserialized.

Also adds a combinatoric fixture for JSON single values within
the dialect-general test suite.

Fixes: #5014
Change-Id: Id38221dce1271fec527ca198b23908547b25d8a0