If the value was wrapped in an existential buffer, we would never
release the original value even though it was passed in at +1.
Fixes <rdar://problem/36153982>, <https://bugs.swift.org/browse/SR-6536>.
The old method of constructing a mangled class name does not work anymore with the new mangling scheme.
Also, by using the re-mangler, _typeByName now works with class names containing non-ascii characters.
For a value of an opaque generic type `<T> x: T`, the language currently defines `type(of: x)` and `T.self` as both producing a type `T.Type`, and the result of substituting an existential type by `T == P` gives `P.Protocol`, so the `type(of:)` operation on `x` can only give the concrete protocol metatype when `x` is an existential in this case. The optimizer understood this rule, but the runtime did not, causing SR-3304.
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.
