Include Schema When Creating Indices

Fixes an issue where indices aren't able to be created for tables in
schemas. At present, `create_index emits SQL like

```sql
CREATE INDEX index_name (col) ON schema_name.table_name
```
which results in an error when creating the table:
```
Index index_name cannot index a table/index schema_name.table_name
which is in a different named schema.
```
because the name needs to be prefixed by schema.

`drop_index` does emit the correct SQL with the schema prefix.
```sql
DROP INDEX schema_name.index_name
```

This is due to an odd issue where the base class's
`visit_create_index` method has in its signature
`include_schema=False`:

https://github.com/sqlalchemy/sqlalchemy/blob/299284cec65076fd4c76bf1efaae60b60f4d4f7b/lib/sqlalchemy/sql/compiler.py#L6828C23-L6828C43

but `visit_drop_index` hard-codes the value to `True`:

https://github.com/sqlalchemy/sqlalchemy/blob/299284cec65076fd4c76bf1efaae60b60f4d4f7b/lib/sqlalchemy/sql/compiler.py#L6870

The dialects handle this by hard-coding `include_schema=True` in
`visit_create_index`, e.g.
sqlite:

https://github.com/sqlalchemy/sqlalchemy/blob/299284cec65076fd4c76bf1efaae60b60f4d4f7b/lib/sqlalchemy/dialects/sqlite/base.py#L1740

The difference in defaults is odd in the base class, but it seems like
include_schema=True is the appropriate setting for Spanner.

Author: waltaskew

google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py

@@ -531,9 +531,7 @@ def post_create_table(self, table):
     def visit_create_index(
         self, create, include_schema=False, include_table_schema=True, **kw
     ):
-        text = super().visit_create_index(
-            create, include_schema, include_table_schema, **kw
-        )
+        text = super().visit_create_index(create, True, include_table_schema, **kw)
         index = create.element
         if "spanner" in index.dialect_options:
             options = index.dialect_options["spanner"]

test/mockserver_tests/test_basics.py

@@ -21,6 +21,7 @@
     MetaData,
     Table,
     Column,
+    Index,
     Integer,
     String,
     func,
@@ -134,6 +135,47 @@ def test_create_table(self):
             requests[0].statements[0],
         )
 
+    def test_create_table_in_schema(self):
+        add_result(
+            """SELECT true
+FROM INFORMATION_SCHEMA.TABLES
+WHERE TABLE_SCHEMA="schema" AND TABLE_NAME="users"
+LIMIT 1
+""",
+            ResultSet(),
+        )
+        engine = create_engine(
+            "spanner:///projects/p/instances/i/databases/d",
+            connect_args={"client": self.client, "pool": FixedSizePool(size=10)},
+        )
+        metadata = MetaData()
+        Table(
+            "users",
+            metadata,
+            Column("user_id", Integer, primary_key=True),
+            Column("user_name", String(16), nullable=False),
+            Index("ix_users_user_id", "user_id"),
+            schema="schema",
+        )
+        metadata.create_all(engine)
+        requests = self.database_admin_service.requests
+        eq_(1, len(requests))
+        is_instance_of(requests[0], UpdateDatabaseDdlRequest)
+        eq_(2, len(requests[0].statements))
+
+        eq_(
+            "CREATE TABLE schema.users (\n"
+            "\tuser_id INT64 NOT NULL "
+            "GENERATED BY DEFAULT AS IDENTITY (BIT_REVERSED_POSITIVE), \n"
+            "\tuser_name STRING(16) NOT NULL\n"
+            ") PRIMARY KEY (user_id)",
+            requests[0].statements[0],
+        )
+        eq_(
+            "CREATE INDEX schema.ix_users_user_id ON schema.users (user_id)",
+            requests[0].statements[1],
+        )
+
     def test_create_multiple_tables(self):
         for i in range(2):
             add_result(