Issue #369: Move isTypeName and isFeatureName to public API

[reckart]

What's in the PR

• Moved the two methods to the public TypeSystemUtil class
• Deprecate them in the old place and mark them for removal in next major version

How to test manually

• No specific test procedure

Automatic testing

• [ ] PR adds/updates unit tests

Documentation

• [ ] PR adds/updates documentation

Organizational

• [ ] PR adds/updates dependencies. _{^{Only dependencies under approved licenses are allowed. LICENSE and NOTICE files in the respective modules where dependencies have been added as well as in the project root have been updated.}}