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/Common/UI/UIController.cpp

@@ -13,6 +13,7 @@
 #include "..\..\EnderDragonRenderer.h"
 #include "..\..\MultiPlayerLocalPlayer.h"
 #include "UIFontData.h"
+#include "UIUnicodeBitmapFont.h"
 #include "UISplitScreenHelpers.h"
 #ifdef _WINDOWS64
 #include "..\..\Windows64\KeyboardMouseInput.h"
@@ -193,6 +194,7 @@ UIController::UIController()
 	m_mcTTFFont = nullptr;
 	m_moj7 = nullptr;
 	m_moj11 = nullptr;
+	m_unicodeBitmapFont = nullptr;
 
 	// 4J-JEV: It's important that these remain the same, unless updateCurrentLanguage is going to be called.
 	m_eCurrentFont = m_eTargetFont = eFont_NotLoaded;
@@ -307,6 +309,14 @@ void UIController::postInit()
 	IggySetAS3ExternalFunctionCallbackUTF16 ( &UIController::ExternalFunctionCallback, this );
 	IggySetTextureSubstitutionCallbacks ( &UIController::TextureSubstitutionCreateCallback , &UIController::TextureSubstitutionDestroyCallback, this );
 
+	// Load a unicode bitmap font as Iggy's global fallback for characters not
+	// covered by the Mojangles bitmap font (CJK, Thai, Arabic, Korean, etc.).
+	// Uses the same glyph page PNGs as the legacy Font class, with matching
+	// Mojangles metrics for correct vertical alignment.
+	m_unicodeBitmapFont = new UIUnicodeBitmapFont("Mojangles_Unicode_Bitmap", SFontData::Mojangles_7);
+	m_unicodeBitmapFont->registerFont();
+	IggyFontSetFallbackFontUTF8("Mojangles_Unicode_Bitmap", -1, IGGY_FONTFLAG_none);
+
 	SetupFont();
 	//
 	loadSkins();