swift234

[deserialization] Unique normal protocol conformances in ASTContext like we do for specialized/inherited protocol conformances.

This fixes the following two bugs:

1. We sometimes would create new conformances when deserializing a
witness method which would not be mapped in the SILModule to the
appropriate witness table. This would cause us to be unable to perform
devirtualization of this witness method. This is tested via a new
verifier check.

2. Different conformances would be created for an instance of a base
protocol and the original protocol. This would cause IRGen to try to
emit witness table global variables with differing types, hitting an
assertion. This is tested via a traditional test.

Swift SVN r15362