Use extension methods instead of properties for convenience methods on IInstantanceDataAccessor

[ivarne]

This is a cleanup effort, because after trying to use IInstanceDataAccessor, I wanted some changes.

The main change is to the interface that gets extension methods instead of a few properties with default implementations.

Interface properties with default implementations has a few drawbacks.

• They need to be mocked individually, because Moq does not use the default implementation
• They typically only serve as a starting point for futher filtering using linq. An extension methdod takes an argument (task/dataType) which is easier to understand than a linq .Where filter.

Another benefit is that we encapsulate appMetadata so that user code has even less reason to deal with dataType

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[sonarcloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
85.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud