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/ClientConnection.cpp

@@ -3315,7 +3315,9 @@ void ClientConnection::handleTileEditorOpen(shared_ptr<TileEditorOpenPacket> pac
 
 void ClientConnection::handleSignUpdate(shared_ptr<SignUpdatePacket> packet)
 {
-	app.DebugPrintf("ClientConnection::handleSignUpdate - ");
+	app.DebugPrintf("[SIGN] handleSignUpdate at (%d, %d, %d):\n", packet->x, packet->y, packet->z);
+	for (int i = 0; i < MAX_SIGN_LINES; i++)
+		app.DebugPrintf("[SIGN]   Line%d: \"%ls\"\n", i+1, packet->lines[i].c_str());
 	if (minecraft->level->hasChunkAt(packet->x, packet->y, packet->z))
 	{
 		shared_ptr<TileEntity> te = minecraft->level->getTileEntity(packet->x, packet->y, packet->z);
@@ -3329,7 +3331,7 @@ void ClientConnection::handleSignUpdate(shared_ptr<SignUpdatePacket> packet)
 				ste->SetMessage(i,packet->lines[i]);
 			}
 
-			app.DebugPrintf("verified = %d\tCensored = %d\n",packet->m_bVerified,packet->m_bCensored);
+			app.DebugPrintf("[SIGN]   verified=%d censored=%d\n", packet->m_bVerified, packet->m_bCensored);
 			ste->SetVerified(packet->m_bVerified);
 			ste->SetCensored(packet->m_bCensored);
 
@@ -3337,12 +3339,12 @@ void ClientConnection::handleSignUpdate(shared_ptr<SignUpdatePacket> packet)
 		}
 		else
 		{
-			app.DebugPrintf("dynamic_pointer_cast<SignTileEntity>(te) == nullptr\n");
+			app.DebugPrintf("[SIGN]   ERROR: tile entity is not a SignTileEntity\n");
 		}
 	}
 	else
 	{
-		app.DebugPrintf("hasChunkAt failed\n");
+		app.DebugPrintf("[SIGN]   ERROR: chunk not loaded at position\n");
 	}
 }