RPL Disp Settings in Model File: Prep: Serialization Strings for two RPL things
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 7.1

Some of the serializations we are dealing with (including in the Registry) 
are using enumerated type integer values.  The revised RPL Display Settings 
serializations (including a new XML-based serialization for inclusion in the 
model file) will want to use serialization strings instead.  These have been 
introduced for these two enumerated types:

  (1) [QtRpl] VisualToken::SymbolType
  (2) RplExpression::Operator_ID

See these new utility methods:

(1) [QtRpl] VisualToken::SymbolType

   static QString getSerializationSymbolTypeStr(SymbolType symbol);
   static SymbolType symbolTypeFromSerializationStr(const QString& str);

(2) RplExpression::Operator_ID

    // Note: Special, newer serialization use only; SEE NOTE IN CODE.
    static QString getSerializationOperatorIdStr( Operator_ID op );
    static Operator_ID operatorIdFromSerializationStr( const QString& str );

Special note for the latter:

RplExpression::Operator_ID
   RplExpression::operatorIdFromSerializationStr(const QString& str)

  // NOTE [Phil, RW 7.1, 4-2017]: The PRIMARY RPL serializations DON'T
  // USE THESE serialization strings; they use the same strings used
  // for display returned by operatorAsString(). These new strings are
  // used for modifications to the RPL Display Settings persistence.

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