Previously we had two separate mechanisms to turn a metatype
into a string. The swift_typeName() function was used to print
the metatype in a human-readable fashion, whereas the
_swift_buildDemanglingForMetadata() was used when naming
generated generic Objective-C classes.
Unify them, since what swift_typeName() does is redundant;
instead of going directly from the metatype to a human-readable
string, we can get the mangling, and print that using the
demangler.
This fixes some issues with unnecessary parenthesis when
printing function types, and also allows Objective-C classes
to be instantiated with nested generic types as parameters.
This allows dynamic casting to succeed between tuple types with
different element types, converting each element in turn. Fixes
rdar://problem/19892202.
When printing a tuple via print(...), print tuple labels when they are
available. This is possible now that the runtime metadata properly
stores tuple labels. Fixes rdar://problem/23130016.
Introduce narrow support for tuple/tuple dynamic casts that merely add
or remove labels, but require the element types to match exactly. This
gets us back to allowing the same correct dynamic casts as in Swift
3.0, when labels were completely ignored.
