Added precision parameter to wxString::From[C]Double().

Optionally support fixed precision in wxString::FromDouble() and FromCDouble()
methods. This is mostly useful for the latter to be able to format numbers in
portable way (using dot as decimal separator) without loss of precision but
also do it for the former for consistency.

Closes #12973.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67181 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/string.h

@@ -1535,29 +1535,37 @@ public:
 
         Unlike FromDouble() the string returned by this function always uses
         the period character as decimal separator, independently of the current
-        locale.
+        locale. Otherwise its behaviour is identical to the other function.
 
         @since 2.9.1
 
         @see ToCDouble()
      */
-    static wxString FromCDouble(double val);
+    static wxString FromCDouble(double val, int precision = -1);
 
     /**
         Returns a string with the textual representation of the number.
 
-        This is a simple wrapper for @code wxString::Format("%g", val)
-        @endcode.
+        For the default value of @a precision, this function behaves as a
+        simple wrapper for @code wxString::Format("%g", val) @endcode. If @a
+        precision is positive (or zero), the @c %.Nf format is used with the
+        given precision value.
 
         Notice that the string returned by this function uses the decimal
         separator appropriate for the current locale, e.g. @c "," and not a
         period in French locale. Use FromCDouble() if this is unwanted.
 
+        @param val
+            The value to format.
+        @param precision
+            The number of fractional digits to use in or -1 to use the most
+            appropriate format. This parameter is new in wxWidgets 2.9.2.
+
         @since 2.9.1
 
         @see ToDouble()
      */
-    static wxString FromDouble(double val);
+    static wxString FromDouble(double val, int precision = -1);
 
     //@{
     /**