swift234

standardize naming of tuples and tuple patterns on "elements".

Previously some parts of the compiler referred to them as "fields",
and most referred to them as "elements".  Use the more generic 'elements'
nomenclature because that's what we refer to other things in the compiler
(e.g. the elements of a bracestmt).

At the same time, make the API better by providing "getElement" consistently
and using it, instead of getElements()[i].

NFC.



Swift SVN r26894