`INTERVAL '1 hour'` should be equivalent to `INTERVAL 1 HOUR`

**Use case**
People are used to Postgres.
node = function_node;
    node->setAlias("@@" + name);
    return true;
}
bool ParserExpressionElement::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    return ParserSubquery().parse(pos, node, expected)
        || ParserTupleOfLiterals().parse(pos, node, expected)
        || ParserParenthesisExpression().parse(pos, node, expected)
        || ParserArrayOfLiterals().parse(pos, node, expected)
        || ParserArray().parse(pos, node, expected)
        || ParserLiteral().parse(pos, node, expected)
        || ParserCastExpression().parse(pos, node, expected)
        || ParserExtractExpression().parse(pos, node, expected)
        || ParserDateAddExpression().parse(pos, node, expected)
        || ParserDateDiffExpression().parse(pos, node, expected)
        || ParserSubstringExpression().parse(pos, node, expected)
        || ParserTrimExpression().parse(pos, node, expected)
        || ParserLeftExpression().parse(pos, node, expected)
        || ParserRightExpression().parse(pos, node, expected)
        || ParserCase().parse(pos, node, expected)
        || ParserColumnsMatcher().parse(pos, node, expected) 
        || ParserFunction().parse(pos, node, expected)
        || ParserQualifiedAsterisk().parse(pos, node, expected)
        || ParserAsterisk().parse(pos, node, expected)
        || ParserCompoundIdentifier().parse(pos, node, expected)
        || ParserSubstitution().parse(pos, node, expected)
        || ParserMySQLGlobalVariable().parse(pos, node, expected);
}
bool ParserWithOptionalAlias::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)