[maps]: Java gRPC Protobuf schemas for Text Search are missing pagination request and response fields

### Summary
The Protobuf schemas exposed by the Java gRPC SDK for **Text Search (New)** do not fully match the official Places API documentation. Pagination-related fields are missing both in `SearchTextRequest` and `SearchTextResponse`, preventing proper pagination support.

### Actual behavior

#### Request
In the Java gRPC Protobuf definition of `SearchTextRequest`, the only available field to limit results is:

```java
SearchTextRequest request = SearchTextRequest.newBuilder()
.setTextQuery("restaurant")
.setMaxResultCount(20)
.build();
```

- `max_result_count` is the only exposed mechanism
- This field is deprecated according to the documentation
- `page_size` and `page_token` are not available in the Protobuf schema

#### Response
`SearchTextResponse` does **not expose `next_page_token`**, making it impossible to retrieve subsequent pages even if pagination were supported on the request side.

### Expected behavior

#### Request
According to the official Places API documentation, pagination should be implemented using `page_size` and `page_token`.

The Protobuf schema should allow usage such as:

```java
SearchTextRequest request = SearchTextRequest.newBuilder()
.setTextQuery("restaurant")
.setPageSize(20)
.setPageToken(pageToken)
.build();
```

#### Response
`SearchTextResponse` should expose `next_page_token` to allow fetching the next page of results:

```java
SearchTextResponse response = placesClient.searchText(request);
String nextPageToken = response.getNextPageToken();
```

### References
- `SearchTextRequest`: https://developers.google.com/maps/documentation/places/web-service/reference/rpc/google.maps.places.v1#searchtextrequest

- `SearchTextResponse`: https://developers.google.com/maps/documentation/places/web-service/reference/rpc/google.maps.places.v1#searchtextresponse