Allow unset data in DescriptorDataBuilder

[ohager]

Is your feature request related to a problem? Please describe.
In a current scenario I need to remove certain elements from the SRC44 Databuilder.

        const oldData = DescriptorData.parse(ledgerAlias.aliasURI, false);
        builder = DescriptorDataBuilder.createWith(oldData);
        // @ts-ignore
        builder.setAlias(undefined)

I needed to ignore Typescript check, when removing alias reference.

Describe the solution you'd like
It could be possible to allow undefined values, but for better readability I recommend to introduce something like unset

        const oldData = DescriptorData.parse(ledgerAlias.aliasURI, false);
        builder = DescriptorDataBuilder.createWith(oldData);
        builder.unsetAlias()