swift234

Have the prechecker pass of the type checker fold T[] and T? expressions when
T is a TypeExpr, forming a larger typeexpr.  We only form TypeExprs in narrow
cases, but this handles the archetype cases in the tests.

This is progress towards:
<rdar://problem/15588967> Array type sugar default construction syntax doesn't work
<rdar://problem/15295763> default constructing an optional fails to typecheck



Swift SVN r16959