Add Get{Min,Max,Range}() to numeric validator classes

Just provide accessors matching the existing setters.

Closes https://github.com/wxWidgets/wxWidgets/pull/1287,
https://github.com/wxWidgets/wxWidgets/pull/1288

interface/wx/valnum.h

@@ -89,6 +89,13 @@ public:
      */
     void SetMin(ValueType min);
 
+    /**
+        Gets the minimal value accepted by the validator.
+
+        @since 3.1.3
+     */
+    ValueType GetMin() const;
+
     /**
         Sets the maximal value accepted by the validator.
 
@@ -96,6 +103,13 @@ public:
      */
     void SetMax(ValueType max);
 
+    /**
+        Gets the maximum value accepted by the validator.
+
+        @since 3.1.3
+     */
+    ValueType GetMax() const;
+
     /**
         Sets both minimal and maximal values accepted by the validator.
 
@@ -103,6 +117,12 @@ public:
      */
     void SetRange(ValueType min, ValueType max);
 
+    /**
+        Gets both minimal and maximal values accepted by the validator.
+
+        @since 3.1.3
+     */
+    void GetRange(ValueType& min, ValueType& max) const;
 
     /**
         Change the validator style.