The ResultSet that is returned by DatabaseMetadata#getTypeInfo has
a column at index 2 with the name DATA_TYPE. This field should
contain one of the java.sql.Types constants, or a vendor-specific
type code. The JDBC specification states that this column should
be a `short` (although the constants in java.sql.Types are of
type `int`).
Cloud Spanner (at the time of writing) does not support any int16
fields. The type code is therefore returned as an int64. The codes
that are used for vendor-specific types by Spanner exceed the max
value of a `short`, and therefore resulted in an OUT_OF_RANGE
exception if you tried to call `ResultSet#getShort(int)` on
this column for any of the Spanner-specific types (e.g. JSON).

This change fixes that by adding an additional vendor type code
for these types that does fit in a `short`. This value is
returned when `getShort(int)` is called on the ResultSet.

Fixes #1688