implemented wxMBConv::IsUTF8() helper for more classes so that all uses of UTF-8 are detected and optimized in wxString

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@46265 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/strconv.h

@@ -223,6 +223,10 @@ public:
         return m_conv->GetMBNulLen();
     }
 
+#if wxUSE_UNICODE_UTF8
+    virtual bool IsUTF8() const { return m_conv->IsUTF8(); }
+#endif
+
     virtual wxMBConv *Clone() const { return new wxConvBrokenFileNames(*this); }
 
 private:
@@ -399,6 +403,10 @@ public:
     virtual size_t WC2MB(char *outputBuf, const wchar_t *psz, size_t outputSize) const;
     virtual size_t GetMBNulLen() const;
 
+#if wxUSE_UNICODE_UTF8
+    virtual bool IsUTF8() const;
+#endif
+
     virtual wxMBConv *Clone() const { return new wxCSConv(*this); }
 
     void Clear();