This PR is part of the effort to implement variable scaled Numeric type (See #2289)

This defined the core type and core functions for handle Numeric.
It is currently no plug to the rest of the code, this will be done in an upcoming PR.

Pull Request Checklist

• Read and understand the contribution guidelines
• Include appropriate tests
• Set a descriptive title and thorough description
• Add a reference to the issue this PR will solve, if appropriate
• Add a line to the release notes, if appropriate
• Normal production system change, include purpose of change in description

NOTE: CI is not automatically run on non-members pull-requests for security
reasons. The reviewer will have to comment with /AzurePipelines run to
trigger the build.