RFC: Choose a syntax for tuple

[andylokandy]

We are going to choose a syntax for tuples from the two:

-- with TUPLE keyword
CREATE TABLE t (name TUPLE(last STRING, first STRING));  -- named
CREATE TABLE t (name TUPLE(STRING, STRING));  -- anonymous
TRY_CAST(col1 AS TUPLE(BIGINT UNSIGNED NULL, BOOLEAN))

-- without TUPLE keyword
CREATE TABLE t (name (last STRING, first STRING));  -- named
CREATE TABLE t (name (STRING, STRING));  -- anonymous
TRY_CAST(col1 AS (BIGINT UNSIGNED NULL, BOOLEAN))

[sundy-li]

The formmer is better.