ENH: improve DynamicList shrink and swapping

- shrink_to_fit()
  corresponds to std::vector naming.
  For DynamicList it is a *binding* request.

- shrink_unsafe()
  simply adjusts the capacity() to match the
  current size() without forcing a re-allocation.

  Useful when collapsing to a non-dynamic list to avoid reallocation
  and copying contents. The memory cleanup will still occur properly
  at a later stage.

- DynamicList::swap(List&)
  simple recovery of content into a non-dynamic List that also
  ensures that the capacity is correctly updated.

STYLE: promote List::capacity() to public visibility (like std::vector)

STYLE: remove unused expandStorage() method

- simply a wrapper for resize(capacity())

applications/test/DynamicList2/Test-DynamicList2.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021-2022 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -144,6 +144,29 @@ int main(int argc, char *argv[])
 
         list1.setCapacity(3);
         printInfo("", list1);
+
+        std::fill_n(std::back_inserter(list1), 10, 5);
+        Info<< "back_inserter to fill some values" << nl;
+        printInfo("", list1);
+
+        // Not very efficient, but just test for capability
+        DynamicList<label, 64> list2;
+
+        list2.resize(5);
+        ListOps::identity(list2);
+
+        Info<< "initial list" << nl;
+        printInfo("", list2);
+
+        labelRange range(10, 5);
+        std::copy(range.begin(), range.end(), std::back_inserter(list2));
+        Info<< "back_inserter to append some values" << nl;
+        printInfo("", list2);
+
+        range.reset(0, 4);
+        std::copy_n(range.begin(), range.size(), std::back_inserter(list2));
+        Info<< "back_inserter to append more values" << nl;
+        printInfo("", list2);
     }
 
     Info<< "\nEnd\n";