Stop using wxWidgets 1.xx wxString compatibility functions

Replace them with std::string-like equivalents when possible (i.e.
replace Length() with length(), IsNull() with empty()) or, at least,
with wx 2 functions if not (e.g. Remove() with Truncate(), First() with
Find(), LowerCase() with MakeLower() etc).

Closes #22638.

utils/wxrc/wxrc.cpp

@@ -622,7 +622,7 @@ static wxString FileToCppArray(wxString filename, int num)
             output << wxT("\n");
         }
         output << tmp;
-        linelng += tmp.Length()+1;
+        linelng += tmp.length()+1;
     }
 
     delete[] buffer;
@@ -780,7 +780,7 @@ static wxString FileToPythonArray(wxString filename, int num)
             output << wxT("\\\n");
         }
         output << tmp;
-        linelng += tmp.Length();
+        linelng += tmp.length();
     }
 
     delete[] buffer;