TextEncoding: add Encode/Decode methods.

This replaces convert_from/to_utf8 in a way that doesn't leak memory.

Use the new method in StyledEdit.

Fixes #6252, #3065.

headers/os/locale/TextEncoding.h

@@ -13,16 +13,32 @@
 #include <stddef.h>
 
 
+struct UConverter;
+
+
 class TextEncoding
 {
 	public:
+		TextEncoding(BString name);
 		TextEncoding(const char* data, size_t length);
 
-		BString GetName();
+		~TextEncoding();
+
+		status_t	InitCheck();
+		BString		GetName();
+
+		status_t Encode(const char* input, size_t& inputLength, char* output,
+			size_t& outputLength);
+		status_t Decode(const char* input, size_t& inputLength, char* output,
+			size_t& outputLength);
+		status_t Flush(char* output, size_t& outputLength);
 
 	private:
 		BString fName;
+
+		UConverter* fUtf8Converter;
+		UConverter* fConverter;
 };
 
 
-#endif /* !TEXTENCODING_H */
+#endif /* TEXTENCODING_H */