Issue Description:

Currently we have these two fixes in the SILParser.

// FIXME: Conformances in InitExistentialRefInst is currently not included
// in SIL.rst.
ResultVal = B.createInitExistentialRef(InstLoc, ExistentialTy,
FormalConcreteTy, Val,
conformances);
break;
}
case ValueKind::InitExistentialMetatypeInst: {
SILType ExistentialTy;
if (parseTypedValueRef(Val, B) ||
P.parseToken(tok::comma, diag::expected_tok_in_sil_instr, ",") ||
parseSILType(ExistentialTy))
return true;

// FIXME: We should be parsing conformances here.
ResultVal = B.createInitExistentialMetatype(InstLoc

We need to parse the conformances here and right some test cases. I have run into the first before, but not the second. I think I have a patch that implements one or the other. I will attach it if I can find it.