WIP: Add alias ["value", 0] in addition to ["argv", 0]

[ivarne]

This ended up being a somewhat larger rewrite. Not sure if I want this now, but it might come up for performance optimisations.

• Move values to a separate interface added to context IContextValueAccessor
• Provide ["value"] as a shortcut for ["dataModel", ["argv", 0]]

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
95.8% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud