[ast] Improve the debug dump for ActorIsolation.

Specifically, I made it so that when one calls dump(), we put in a newline
afterwards so we get a nice easy to read msg in the debugger. I also defined
dumpForDiagnostics() to make it easy to dump out in the debugger how the
ActorIsolation will show up in the diagnostics.

Author: gottesmm

include/swift/AST/ActorIsolation.h

@@ -286,7 +286,15 @@ class ActorIsolation {
   void printForDiagnostics(llvm::raw_ostream &os,
                            StringRef openingQuotationMark = "'") const;
 
-  SWIFT_DEBUG_DUMP { print(llvm::dbgs()); }
+  SWIFT_DEBUG_DUMP {
+    print(llvm::dbgs());
+    llvm::dbgs() << '\n';
+  }
+
+  SWIFT_DEBUG_DUMPER(dumpForDiagnostics()) {
+    printForDiagnostics(llvm::dbgs());
+    llvm::dbgs() << '\n';
+  }
 };
 
 /// Determine how the given value declaration is isolated.