Reduce array abstraction on apple platforms dealing with literals (#13665)

* Reduce array abstraction on apple platforms dealing with literals

Part of the ongoing quest to reduce swift array literal abstraction
penalties: make the SIL optimizer able to eliminate bridging overhead
 when dealing with array literals.

Introduce a new classify_bridge_object SIL instruction to handle the
logic of extracting platform specific bits from a Builtin.BridgeObject
value that indicate whether it contains a ObjC tagged pointer object,
or a normal ObjC object. This allows the SIL optimizer to eliminate
these, which allows constant folding a ton of code. On the example
added to test/SILOptimizer/static_arrays.swift, this results in 4x
less SIL code, and also leads to a lot more commonality between linux
and apple platform codegen when passing an array literal.

This also introduces a couple of SIL combines for patterns that occur
in the array literal passing case.

lib/Serialization/SerializeSIL.cpp

@@ -1112,6 +1112,7 @@ void SILSerializer::writeSILInstruction(const SILInstruction &SI) {
   case SILInstructionKind::LoadUnownedInst:
   case SILInstructionKind::LoadWeakInst:
   case SILInstructionKind::MarkUninitializedInst:
+  case SILInstructionKind::ClassifyBridgeObjectInst:
   case SILInstructionKind::FixLifetimeInst:
   case SILInstructionKind::EndLifetimeInst:
   case SILInstructionKind::CopyBlockInst: