[send-non-sendable] Make sure that we translate project_box into the pseudo-IR.

This is a case of an instruction that we missed translating into the pseudo-IR.
This was easy to do since we are not yet performing an exhaustive switch over
all instruction kinds when translating. Earlier I did the first part of the
translation by switching from doing conditional is<INST> to switch but haven't
yet eliminated the default yet from the switch. I am fixing this now since with
my load [copy] change from earlier causes us to crash in the earlier unorganized
tests.

rdar://115367810

Author: gottesmm

lib/SILOptimizer/Mandatory/SendNonSendable.cpp

@@ -770,6 +770,7 @@ class PartitionOpTranslator {
     case SILInstructionKind::PointerToAddressInst:
     case SILInstructionKind::ProjectBlockStorageInst:
     case SILInstructionKind::RefElementAddrInst:
+    case SILInstructionKind::ProjectBoxInst:
     case SILInstructionKind::RefToUnmanagedInst:
     case SILInstructionKind::StrongCopyUnownedValueInst:
     case SILInstructionKind::StructElementAddrInst:

test/Concurrency/sendnonsendable_basic.swift

@@ -0,0 +1,32 @@
+// RUN: %target-swift-frontend -emit-sil -strict-concurrency=complete -enable-experimental-feature SendNonSendable -disable-availability-checking -verify %s -o /dev/null
+
+// REQUIRES: concurrency
+// REQUIRES: asserts
+
+////////////////////////
+// MARK: Declarations //
+////////////////////////
+
+/// Classes are always non-sendable, so this is non-sendable
+class NonSendableKlass {
+  func asyncCall() async {}
+}
+
+actor Actor {
+  var klass = NonSendableKlass()
+  final var finalKlass = NonSendableKlass()
+}
+
+final actor FinalActor {
+  var klass = NonSendableKlass()
+}
+
+/////////////////////////////
+// MARK: Closure Formation //
+/////////////////////////////
+
+// This test makes sure that we can properly pattern match project_box.
+func formClosureWithoutCrashing() {
+  var c = NonSendableKlass() // expected-warning {{variable 'c' was never mutated; consider changing to 'let' constant}}
+  let _ = { print(c) }
+}