ENH: add ListPolicy::reserve_size() helper (related to #3348)

- central way to calculate reverse sizes for dynamic containers.

  For example;
      reserve_size<16, 2>(len, cap);     // min-size=16, ratio=2
      reserve_size<16, 3, 2>(len, cap);  // min-size=16, ratio=1.5

  replaces this type of code that was used in several places:
      max(SizeMin, max(len, label(2*capacity_)));

  The caller will have already checked (len < cap) before deciding
  to make this call.

ENH: updates for DynamicList/DynamicField handling

- add reserve_exact() method, which is like reserve() but without any
  extra sizing heuristics

- add DynamicField 'reuse' constructors, consistent with Field constructors

- sync allocated size before list destruction.
  This may help when using aligned allocation strategies.

applications/test/CircularBuffer/Make/files

@@ -1,3 +1,3 @@
-Test-CircularBuffer.C
+Test-CircularBuffer.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-CircularBuffer

applications/test/List/Test-List.cxx

@@ -140,8 +140,46 @@ int main(int argc, char *argv[])
     argList::addBoolOption("ListList", "Test list of list functionality");
     argList::addBoolOption("flag");
 
+    argList::addBoolOption("reserve", "Test ListPolicy for reserve_size");
+
     #include "setRootCase.H"
 
+    if (args.found("reserve"))
+    {
+        using namespace Foam::ListPolicy;
+
+        using control = std::pair<label, label>;
+
+        for
+        (
+            const auto& tup :
+            {
+                control{ 10, 5 },
+                control{ 20, 25 }
+            }
+        )
+        {
+            const auto [len, capacity] = tup;
+
+            Info<< "test " << tup << nl;
+
+            auto size = reserve_size<16,2>(len, capacity);
+            Info<< "   => " << size << " (ratio 2)" << nl;
+
+            size = reserve_size<16,3,2>(len, capacity);
+            Info<< "   => " << size << " (ratio 3/2)" << nl;
+
+            size = reserve_size<16,13,8>(len, capacity);
+            Info<< "   => " << size << " (ratio " << (13.0/8) << ')' << nl;
+
+            size = reserve_size<16,25,16>(len, capacity);
+            Info<< "   => " << size << " (ratio " << (25.0/16) << ')' << nl;
+        }
+
+        Info<< nl << "\nEnd" << endl;
+        return 0;
+    }
+
     {
         List<label> ident(15);
         Foam::identity(ident, 0);