CSV import: explicit column-to-property mapping

[amirrza777]

Summary

Follow-up to #12. CSV import currently matches CSV columns to metamodel properties by name only. There's no way to map a column with a different name to a property, or to skip columns.

Proposed Feature

Extend the import CSV { ClassName from "file.csv" } syntax with an optional explicit mapping, e.g.:

import CSV {
    Person from "employees.csv" {
        csvColumnName -> modelPropertyName
    }
}

Name-based matching should remain the default when no explicit mapping is given.

Scope

Deferred out of the main CSV import PR per Niklas and Steffen's feedback on #12. Name-based matching alone is sufficient for that PR.