[region-isolation] Avoid using the function isolation when determining isolation of a sil_isolated parameter.

It is unnecessary and seems to be slightly out of sync sometimes around
closures.

(cherry picked from commit c1d0c8c)

Author: gottesmm

lib/SIL/Verifier/SILVerifier.cpp

@@ -6577,6 +6577,13 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
                                     SILResultInfo::IsTransferring);
                               })),
             "transferring result means all results are transferring");
+
+    // We should only ever have a single sil_isolated parameter.
+    require(1 >= std::count_if(FTy->getParameters().begin(), FTy->getParameters().end(),
+                               [](const SILParameterInfo &parameterInfo) {
+                                 return parameterInfo.hasOption(SILParameterInfo::Isolated);
+                               }),
+            "Should only ever be isolated to a single parameter");
   }
 
   struct VerifyFlowSensitiveRulesDetails {

lib/SILOptimizer/Utils/PartitionUtils.cpp

@@ -416,13 +416,10 @@ SILIsolationInfo SILIsolationInfo::get(SILArgument *arg) {
   // Before we do anything further, see if we have an isolated parameter. This
   // handles isolated self and specifically marked isolated.
   if (auto *isolatedArg = fArg->getFunction()->maybeGetIsolatedArgument()) {
-    if (auto functionIsolation = fArg->getFunction()->getActorIsolation()) {
-      assert(functionIsolation.isActorInstanceIsolated());
-      if (auto *nomDecl =
-              isolatedArg->getType().getNominalOrBoundGenericNominal()) {
-        return SILIsolationInfo::getActorInstanceIsolated(fArg, isolatedArg,
-                                                          nomDecl);
-      }
+    if (auto *nomDecl =
+        isolatedArg->getType().getNominalOrBoundGenericNominal()) {
+      return SILIsolationInfo::getActorInstanceIsolated(fArg, isolatedArg,
+                                                        nomDecl);
     }
   }