Missing INFORMATION_SCHEMA.INDEXES.SEARCH_(PARTITION_BY|ORDER_BY)

These columns are missing in `INFORMATION_SCHEMA.INDEXES`.
- `SEARCH_PARTITION_BY`
- `SEARCH_ORDER_BY`

In cloud-spanner-emulator v1.5.52:

```
spanner> DESCRIBE SELECT * FROM INFORMATION_SCHEMA.INDEXES;
+---------------------+---------------+
| Column_Name | Column_Type |
+---------------------+---------------+
| TABLE_CATALOG | STRING |
| TABLE_SCHEMA | STRING |
| TABLE_NAME | STRING |
| INDEX_NAME | STRING |
| INDEX_TYPE | STRING |
| PARENT_TABLE_NAME | STRING |
| IS_UNIQUE | BOOL |
| IS_NULL_FILTERED | BOOL |
| INDEX_STATE | STRING |
| FILTER | STRING |
| SPANNER_IS_MANAGED | BOOL |
| SEARCH_PARTITION_BY | ARRAY |
| SEARCH_ORDER_BY | ARRAY |
+---------------------+---------------+
```

In real instance:

```
spanner> DESCRIBE SELECT * FROM INFORMATION_SCHEMA.INDEXES;
+--------------------+-------------+
| Column_Name | Column_Type |
+--------------------+-------------+
| TABLE_CATALOG | STRING |
| TABLE_SCHEMA | STRING |
| TABLE_NAME | STRING |
| INDEX_NAME | STRING |
| INDEX_TYPE | STRING |
| PARENT_TABLE_NAME | STRING |
| IS_UNIQUE | BOOL |
| IS_NULL_FILTERED | BOOL |
| INDEX_STATE | STRING |
| SPANNER_IS_MANAGED | BOOL |
+--------------------+-------------+
```

## Note
* These columns are not yet documented in https://docs.cloud.google.com/spanner/docs/information-schema#indexes.
* Related: #330