Return the normalized field name for the given AST node.

def get_ast_field_name(ast):
    """Return the normalized field name for the given AST node."""
    replacements = {
        # We always rewrite the following field names into their proper underlying counterparts.
        TYPENAME_META_FIELD_NAME: '@class'
    }
    base_field_name = ast.name.value
    normalized_name = replacements.get(base_field_name, base_field_name)
    return normalized_name