feat: add support for PG.OID in parameterized queries

[larkee]

This PR adds support for using PG.OID values in parameterized SELECT queries.

For example:

with database.snapshot() as snapshot:
results = snapshot.execute_sql(
"SELECT $1",
params = {"p1": 123},
param_types = {"p1": spanner.param_types.PG_OID})
for row in results:
print(row)