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.World/SignTileEntity.cpp

@@ -50,11 +50,10 @@ void SignTileEntity::save(CompoundTag *tag)
 	tag->putString(L"Text3", m_wsmessages[2] );
 	tag->putString(L"Text4", m_wsmessages[3] );
 #ifndef _CONTENT_PACKAGE
-	OutputDebugStringW(L"### - Saving a sign with text - \n");
+	app.DebugPrintf("[SIGN] Saving sign at (%d, %d, %d):\n", x, y, z);
 	for(int i=0;i<4;i++)
 	{
-		OutputDebugStringW(m_wsmessages[i].c_str());
-		OutputDebugStringW(L"\n");
+		app.DebugPrintf("[SIGN]   Line%d: \"%ls\"\n", i+1, m_wsmessages[i].c_str());
 	}
 #endif
 }
@@ -65,8 +64,8 @@ void SignTileEntity::load(CompoundTag *tag)
 	TileEntity::load(tag);
 	for (int i = 0; i < MAX_SIGN_LINES; i++) 
 	{
-		wchar_t *buf = new wchar_t[256];
-		swprintf(buf, 256, L"Text%d", (i+1) );
+		wchar_t buf[16];
+		swprintf(buf, 16, L"Text%d", (i+1) );
 		m_wsmessages[i] = tag->getString( buf );
 		if (m_wsmessages[i].length() > MAX_LINE_LENGTH) m_wsmessages[i] = m_wsmessages[i].substr(0, MAX_LINE_LENGTH);
 	}