Fix handling of road access restrictions

[sfendrich]

Problem description

Road access restrictions are accumulated over all tag keys instead of respecting the tag-key hierarchy.

Proposed solution

• Access should be processed according to the key hierarchy, e.g., the access tagged with key motorcar should overwrite an access tagged via vehicle
• Multiple values in one tag should be considered, e.g., access=private;customers
• Adapt AccessRestrictionParserTest expectations, refactor into parametrized test