Adds support for parsing fileMappings and calculating the goal state from them.
Adds support for fileMappings to the schema. Includes a schema validation error if the schema uses fileMappings but doesn't have a sufficiently high version set.
Enables manifest version "3.0" and sets that as the default for newly created manifests.
This implements #738. There will be an additional PR to make the JSON completion in the editor work for fileMappings.
Summary of the changes:
This implements #738. There will be an additional PR to make the JSON completion in the editor work for fileMappings.