Intellisense autocompletion for derivative package

[kevinbbbb]

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Pre-checks*

Please change the following [ ] to [x] for confirmation.

• [x] The feature request has not been suggested in this repository.

The Missed*

Is your feature request related to a problem? Please provide a clear and concise description of what the problem is.

• no Intellisense autocompletion is available for commands of the derivative package, which is a feature-rich package for writing derivatives, differentials etc.

The Solution*

Please provide a solution you would like to have.

• add Intellisense autocompletion for the derivative package

Anything Else?

Add any other context about the feature request below.

• a .cwl file for this package is available at https://github.com/texstudio-org/texstudio/blob/master/completion/derivative.cwl