Add support for a standard TupleType. Though this is a standard type, it...

Add support for a standard TupleType. Though this is a standard type, it merely provides a common mechanism for representing tuples in MLIR. It is up to dialect authors to provides operations for manipulating them, e.g. extract_tuple_element.

TupleType has the following form:
   tuple-type ::= `tuple` `<` (type (`,` type)*)? `>`

Example:

// Empty tuple.
tuple<>

// Single element.
tuple<i32>

// Multi element.
tuple<i32, tuple<f32>, i16>

PiperOrigin-RevId: 239226021