ENH: direct support for broadcast of bitSet

- the internal data are contiguous so can broadcast size and internals
  directly without an intermediate stream.

ENH: split out broadcast time for profilingPstream information

STYLE: minor Pstream cleanup

- UPstream::commsType_ from protected to private, since it already has
  inlined noexcept getters/setters that should be used.

- don't pass unused/unneed tag into low-level MPI reduction templates.
  Document where tags are not needed

- had Pstream::broadcast instead of UPstream::broadcast in internals

applications/test/parallel-broadcast/Test-parallel-broadcast.C

@@ -34,6 +34,7 @@ Description
 #include "List.H"
 #include "argList.H"
 #include "Time.H"
+#include "bitSet.H"
 #include "vector.H"
 #include "IPstream.H"
 #include "OPstream.H"
@@ -74,6 +75,16 @@ void testBroadcast(List<T>& values)
 }
 
 
+void testBroadcast(bitSet& values)
+{
+    Pout<< "pre-broadcast: "
+        << values.size() << ": " << flatOutput(values.values()) << endl;
+    Pstream::broadcast(values);
+    Pout<< "post-broadcast: "
+        << values.size() << ": " << flatOutput(values.values()) << endl;
+}
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 int main(int argc, char *argv[])
@@ -149,6 +160,22 @@ int main(int argc, char *argv[])
         testBroadcast(values);
     }
 
+    {
+        bitSet values;
+        if (Pstream::master())
+        {
+            values.set(labelList({1, 4, 8}));
+            values.resize(10);
+        }
+        else
+        {
+            // Just something different
+            values.set(labelList({0, 2}));
+            values.resize(5);
+        }
+        testBroadcast(values);
+    }
+
     Info<< "End\n" << endl;
 
     return 0;