feat: add builder / copy method to google.cloud.bigquery.query.ScalarQueryParameterType that makes a copy with a new name #642

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

When constructing a StructQueryParameterType, it is necessary to pass in types for sub-fields. We have created a SqlParameterScalarTypes enum to make this easier, but often times a struct's sub-fields are named. In this case, the enum values are less useful.

Describe the solution you'd like

It'd be helpful to construct a type for the struct sub-fields by using the enum classes. Perhaps

google.cloud.bigquery.enums.SqlParameterScalarTypes.STRING.with_name("first_name")

could create a copy of google.cloud.bigquery.enums.SqlParameterScalarTypes.STRING, but with the name field populated?

Describe alternatives you've considered

Possible that the SqlParameterScalarTypes enum was unnecessary, but it's part of our public interface now.

Additional context

#633 (comment)