swift234

Fix <rdar://problem/23700031> QoI: Terrible diagnostic in tuple assignment

When inferring a contextual type for the input expression to an assignment,
use getRValueType() to strip lvalues from tuple types in recursive positions,
this allows us to produce a sensible diagnostic of:

error: binary operator '%' cannot be applied to two 'T' operands

instead of:

error: cannot assign value of type 'T' to type '@lvalue _'

because we don't have a weird lvalue type in the way.