ENH: disentangle testing and quoting of regex characters

- originally had tests for regex meta characters strewn across
  regExp classes as well as wordRe, keyType, string.
  And had special-purpose quotemeta static function within string
  that relied on special naming convention for testing the meta
  characters.

  The regex meta character testing/handling now relegated entirely
  to the regExp class(es).
  Relocate quotemeta to stringOps, with a predicate.

- avoid code duplication. Reuse some regExpCxx methods in regExpPosix

src/OpenFOAM/primitives/strings/stringOps/stringOps.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2012 OpenFOAM Foundation
-    Copyright (C) 2016-2020 OpenCFD Ltd.
+    Copyright (C) 2016-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -77,6 +77,15 @@ namespace stringOps
         return wordRes::matcher(patterns)(text);
     }
 
+    //- Quote any meta-characters in given string
+    template<class StringType, class UnaryPredicate>
+    StringType quotemeta
+    (
+        const StringType& str,
+        const UnaryPredicate& meta,
+        const char quote = '\\'
+    );
+
     //- Expand occurrences of variables according to the mapping
     //- and return the expanded string.
     //