Enable multi-language font rendering and Unicode text input

Goal:
Allow players to type and display text in any language supported by
Unicode, including Chinese, Japanese, Korean, Thai, Arabic, Korean, Hindi, and more. This
covers all text surfaces: chat editor, chat messages, signs (in-world
and editor), world name/seed, server address/port fields, and all
Iggy Flash UI text fields.

Multi-language support:
Two complementary rendering systems were added to handle Unicode text
across the entire client:

1. Iggy UI (Flash-based text fields): A new UIUnicodeBitmapFont class
   serves Java Minecraft's glyph page PNGs (glyph_00.png-glyph_FF.png)
   through Iggy's bitmap font provider API. Registered as the global
   fallback font with metrics matching the Mojangles bitmap font for
   correct baseline alignment. When the primary bitmap font lacks a
   glyph, it returns IGGY_GLYPH_INVALID and Iggy seamlessly falls back
   to the unicode bitmap font.

2. Legacy C++ Font renderer (chat editor, in-world signs): Revived the
   commented-out unicode glyph page system in Font.cpp. Characters not
   in the bitmap font texture are rendered from glyph page PNGs loaded
   on demand, with proper texture switching mid-string.

3. ChatScreen input: Removed the restrictive acceptableLetters filter
   so all printable Unicode characters are accepted in chat.

Languages now supported for text input and rendering:
- Japanese (Hiragana, Katakana, Kanji)
- Chinese (Simplified and Traditional)
- Korean (Hangul)
- Thai
- Arabic
- Hindi (Devanagari)
- Russian (Cyrillic) - already worked via bitmap font
- Greek - already worked via bitmap font
- Polish, Czech, Turkish (Extended Latin) - already worked via bitmap font
- Armenian, Georgian, and other scripts covered by glyph pages

Security fixes:
- Fixed memset under-initialization of Font::charWidths (zeroed 460
  bytes instead of 460*sizeof(int)=1840 bytes, leaving entries 115+
  uninitialized) - pre-existing bug
- Added bounds checks to all UIUnicodeBitmapFont callbacks to reject
  glyph IDs outside [0, 65535], preventing OOB array access
- Added bounds check in Font::width() section-sign fallback path to
  prevent OOB read on charWidths[] with high codepoints
- Blocked Unicode bidirectional override characters (U+202A-202E,
  U+2066-2069) in chat input to prevent message spoofing

Memory leak fix:
- Fixed SignTileEntity::load allocating wchar_t[256] with new[] on
  every sign load without freeing. Replaced with stack allocation.

Debug logging:
- Added [SIGN] prefixed logging for sign save/update operations
- Added [CHAT] prefixed logging for chat send/receive operations

Files changed:
- UIUnicodeBitmapFont.h/.cpp (new) - Iggy bitmap font for glyph pages
- UIBitmapFont.cpp - Return IGGY_GLYPH_INVALID for unknown chars
- UIFontData.h/.cpp - Added hasGlyph() method
- UIController.h/.cpp - Load and register unicode bitmap fallback font
- UITTFFont.h/.cpp - Added registerAsDefaultFonts parameter
- Font.h/.cpp - Revived unicode glyph page rendering system
- ChatScreen.cpp - Accept all Unicode input, block bidi overrides
- Gui.cpp - Chat display debug logging
- ClientConnection.cpp - Sign update debug logging
- SignTileEntity.cpp - Sign save logging, memory leak fix

Minecraft.Client/ChatScreen.cpp

@@ -14,7 +14,12 @@ wstring ChatScreen::s_historyDraft;
 
 bool ChatScreen::isAllowedChatChar(wchar_t c)
 {
-	return c >= 0x20 && (c == L'\u00A7' || allowedChars.empty() || allowedChars.find(c) != wstring::npos);
+	if (c < 0x20) return false;
+	// Block Unicode bidirectional override characters that can be used to
+	// spoof chat messages or impersonate players.
+	if (c >= 0x202A && c <= 0x202E) return false; // LRE, RLE, PDF, LRO, RLO
+	if (c >= 0x2066 && c <= 0x2069) return false; // LRI, RLI, FSI, PDI
+	return true;
 }
 
 ChatScreen::ChatScreen()
@@ -93,6 +98,9 @@ void ChatScreen::keyPressed(wchar_t ch, int eventKey)
     if (eventKey == Keyboard::KEY_RETURN)
 	{
         wstring trim = trimString(message);
+        { char buf[64]; sprintf_s(buf, "[CHAT] Sending (%d chars): ", (int)trim.length()); OutputDebugStringA(buf); }
+        OutputDebugStringW(trim.c_str());
+        OutputDebugStringA("\n");
         if (trim.length() > 0)
 		{
             if (!minecraft->handleClientSideCommand(trim))
@@ -135,6 +143,7 @@ void ChatScreen::keyPressed(wchar_t ch, int eventKey)
 	{
         message.insert(cursorIndex, 1, ch);
         cursorIndex++;
+        { char buf[64]; sprintf_s(buf, "[CHAT] Char U+%04X accepted (%d chars)\n", (unsigned)ch, (int)message.length()); OutputDebugStringA(buf); }
     }
 }