LibTextCodec: Add IBM866 decoder

Userland/Libraries/LibTextCodec/Decoder.cpp

@@ -28,6 +28,17 @@ TurkishDecoder s_turkish_decoder;
 XUserDefinedDecoder s_x_user_defined_decoder;
 
 // clang-format off
+// https://encoding.spec.whatwg.org/index-ibm866.txt
+SingleByteDecoder s_ibm866_decoder {{
+    0x0410, 0x0411, 0x0412, 0x0413, 0x0414, 0x0415, 0x0416, 0x0417, 0x0418, 0x0419, 0x041A, 0x041B, 0x041C, 0x041D, 0x041E, 0x041F,
+    0x0420, 0x0421, 0x0422, 0x0423, 0x0424, 0x0425, 0x0426, 0x0427, 0x0428, 0x0429, 0x042A, 0x042B, 0x042C, 0x042D, 0x042E, 0x042F,
+    0x0430, 0x0431, 0x0432, 0x0433, 0x0434, 0x0435, 0x0436, 0x0437, 0x0438, 0x0439, 0x043A, 0x043B, 0x043C, 0x043D, 0x043E, 0x043F,
+    0x2591, 0x2592, 0x2593, 0x2502, 0x2524, 0x2561, 0x2562, 0x2556, 0x2555, 0x2563, 0x2551, 0x2557, 0x255D, 0x255C, 0x255B, 0x2510,
+    0x2514, 0x2534, 0x252C, 0x251C, 0x2500, 0x253C, 0x255E, 0x255F, 0x255A, 0x2554, 0x2569, 0x2566, 0x2560, 0x2550, 0x256C, 0x2567,
+    0x2568, 0x2564, 0x2565, 0x2559, 0x2558, 0x2552, 0x2553, 0x256B, 0x256A, 0x2518, 0x250C, 0x2588, 0x2584, 0x258C, 0x2590, 0x2580,
+    0x0440, 0x0441, 0x0442, 0x0443, 0x0444, 0x0445, 0x0446, 0x0447, 0x0448, 0x0449, 0x044A, 0x044B, 0x044C, 0x044D, 0x044E, 0x044F,
+    0x0401, 0x0451, 0x0404, 0x0454, 0x0407, 0x0457, 0x040E, 0x045E, 0x00B0, 0x2219, 0x00B7, 0x221A, 0x2116, 0x00A4, 0x25A0, 0x00A0,
+}};
 // https://encoding.spec.whatwg.org/index-windows-1250.txt
 SingleByteDecoder s_centraleurope_decoder {{
     0x20AC, 0x0081, 0x201A, 0x0083, 0x201E, 0x2026, 0x2020, 0x2021, 0x0088, 0x2030, 0x0160, 0x2039, 0x015A, 0x0164, 0x017D, 0x0179,
@@ -99,6 +110,8 @@ Optional<Decoder&> decoder_for(StringView a_encoding)
             return s_utf16be_decoder;
         if (encoding.value().equals_ignoring_ascii_case("utf-16le"sv))
             return s_utf16le_decoder;
+        if (encoding.value().equals_ignoring_ascii_case("ibm866"sv))
+            return s_ibm866_decoder;
         if (encoding.value().equals_ignoring_ascii_case("iso-8859-2"sv))
             return s_latin2_decoder;
         if (encoding.value().equals_ignoring_ascii_case("windows-1250"sv))