Is your feature request related to a problem? Please describe.

As part of #3130, the TableResult class got refactored from a class with a constructor, into an abstract class with a builder.

Since TableResult is the object one receives back when using BigQuery::query(), then we receive and can use the TableResult class.

Also as part of #3130, the string marker "Exposed for testing" was removed from the @InternalAPI annotation that was there before.
Since we write our tests to simply mock the BigQuery class and construct a response (TableResult), this worked fine with the new builder methods - although since this was exposed and the class is part of the API, a breaking change like this should probably have been rolled out more delicately.

Describe the solution you'd like

Remove @InternalApi annotation from TableResult since the class is part of the API - this should also prevent maintainers from making breaking changes to it in the future.