Make ActorIsolation on SILFunction non-optional.

ActorIsolation already has a "I have no value case": unspecified. Lets just use
that.

Just a mistake I made that I am trying to fix before anything further depends on
this code.

Author: gottesmm

include/swift/SIL/SILFunction.h

@@ -348,7 +348,7 @@ class SILFunction
   unsigned BlockListChangeIdx = 0;
 
   /// The isolation of this function.
-  std::optional<ActorIsolation> actorIsolation;
+  ActorIsolation actorIsolation = ActorIsolation::forUnspecified();
 
   /// The function's bare attribute. Bare means that the function is SIL-only
   /// and does not require debug info.
@@ -1374,9 +1374,7 @@ class SILFunction
     actorIsolation = newActorIsolation;
   }
 
-  std::optional<ActorIsolation> getActorIsolation() const {
-    return actorIsolation;
-  }
+  ActorIsolation getActorIsolation() const { return actorIsolation; }
 
   //===--------------------------------------------------------------------===//
   // Block List Access

include/swift/SILOptimizer/Utils/PartitionUtils.h

@@ -901,8 +901,8 @@ struct PartitionOpEvaluator {
       // our transferring operand. If so, we can squelch this.
       if (auto functionIsolation =
               transferringOp->getUser()->getFunction()->getActorIsolation()) {
-        if (functionIsolation->isActorIsolated() &&
-            SILIsolationInfo::getActorIsolated(*functionIsolation) ==
+        if (functionIsolation.isActorIsolated() &&
+            SILIsolationInfo::getActorIsolated(functionIsolation) ==
                 SILIsolationInfo::get(transferringOp->getUser()))
           return;
       }

lib/SILOptimizer/Utils/PartitionUtils.cpp

@@ -91,7 +91,7 @@ SILIsolationInfo SILIsolationInfo::get(SILFunctionArgument *arg) {
   // should be marked as actor isolated.
   if (auto *self = arg->getFunction()->maybeGetSelfArgument()) {
     if (auto functionIsolation = arg->getFunction()->getActorIsolation()) {
-      if (functionIsolation->isActorIsolated()) {
+      if (functionIsolation.isActorIsolated()) {
         if (auto *nomDecl = self->getType().getNominalOrBoundGenericNominal()) {
           if (auto isolationInfo =
                   SILIsolationInfo::getActorIsolated(nomDecl)) {