STYLE: use spanstream instead of stringstream in more places

- particularly useful in these combinations:

  1.
      OCharStream buf;
      // populate

      ISpanStream is(buf.view());
      // parse

  2.
      // read from file
      ifile.getLine(str);

      ISpanStream is(str);
      // parse

  These avoid making a copy of the character content, compared to
  versions with stringstream:

      OStringStream buf;
      IStringStream is(buf.str());

applications/utilities/thermophysical/chemkinToFoam/chemkinToFoam.C

@@ -99,9 +99,11 @@ int main(int argc, char *argv[])
     // Temporary hack to splice the specie composition data into the thermo file
     // pending complete integration into the thermodynamics structure
 
-    OStringStream os;
+    OCharStream os;
     cr.speciesThermo().write(os);
-    dictionary thermoDict(IStringStream(os.str())());
+
+    ISpanStream is(os.view());
+    dictionary thermoDict(is);
 
     // Add elements
     for (entry& dEntry : thermoDict)