Cover more of the Azure SDK types with the default operation tests

[antkmsft]

Take the approach of #4627, which introduced a test helper class, and adds coverage for ETag type, and cover more of the Azure SDK types using that helper class.

People are free to take as big chunk of work as they want - we'll create a sub-issue with corresponding smaller scope, and will mention contributors in the CHANGELOG.

Ultimately, we want all the SDK types to be covered - structs and classes, from all our libraries.

[antkmsft]

For the information, a more recent PR #4822 does cover more of the Azure Core types (but probably not all of them, so the issue remains open).