Convert wide chars before reading model

The PEGTL parser used by KiCad for SPICE models only handles ASCII
characters.  Despite the docs stating that you can, in theory, parse a
UTF-8 character by reading the base string, in pratice this does not
work as the UTF-8 string is represented by unsigned chars and the PEGTL
string is based on signed char.

To work around this, we need to convert micro and mu to the ASCII 'u'
equivalent

Fixes https://gitlab.com/kicad/code/kicad/issues/13642

eeschema/sim/sim_model.cpp

@@ -1107,6 +1107,11 @@ bool SIM_MODEL::InferSimModel( T_symbol& aSymbol, std::vector<T_field>* aFields,
     auto convertNotation =
             [&]( const wxString& units ) -> wxString
             {
+                /// KiCad Spice PEGTL only handles ASCII
+                /// Although these two look the same, they are U+03BC and U+00B5
+                if( units == wxS( "µ" ) || units == wxS( "μ" ) )
+                    return wxS( "u" );
+
                 if( aNotation == SIM_VALUE_GRAMMAR::NOTATION::SPICE )
                 {
                     if( units == wxT( "M" ) )