swift234

Teach SerializedSILLoader how to load all SILFunctions. Also add SerializedSILLoader::getAll().

getAll deserializes all SIL (except for globals). This enables us to iterate
over the SILModules once instead of once for first SILFunctions, then VTables,
then WitnessTables which is just inefficient.

Swift SVN r14176