[21.0] add new datatype class for meryldb

[bgruening]

What did you do?

• [describe the proposed changes]

Why did you make this change?

(Cite Issue number OR provide rationalization of changes if no issue exists)
(If fixing a bug, please add any relevant error or traceback)

How to test the changes?

(select the most appropriate option; if the latter, provide steps for testing below)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

For UI Components

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[github-actions]

This PR was merged without a "kind/" label, please correct.