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/UIBitmapFont.cpp

@@ -141,6 +141,9 @@ S32 UIBitmapFont::GetCodepointGlyph(U32 codepoint)
 	// 4J-JEV: Change "right single quotation marks" to apostrophies.
 	if (codepoint == 0x2019) codepoint = 0x27;
 
+	if (!m_cFontData->hasGlyph(codepoint))
+		return IGGY_GLYPH_INVALID;
+
 	return m_cFontData->getGlyphId(codepoint);
 }
 
@@ -253,19 +256,6 @@ rrbool UIBitmapFont::GetGlyphBitmap(S32 glyph,F32 pixel_scale,IggyBitmapCharacte
 	while ( (0.5f + glyphScale) * truePixelScale < pixel_scale)
 		glyphScale++;
 
-	// Debug: log each unique (font, pixel_scale) pair
-	{
-		static std::unordered_set<int> s_loggedScaleKeys;
-		// Encode font pointer + quantized scale into a key to log each combo once
-		int scaleKey = (int)(pixel_scale * 100.0f) ^ (int)(uintptr_t)m_cFontData;
-		if (s_loggedScaleKeys.find(scaleKey) == s_loggedScaleKeys.end() && s_loggedScaleKeys.size() < 50) {
-			s_loggedScaleKeys.insert(scaleKey);
-			float tps = truePixelScale;
-			app.DebugPrintf("[FONT-DBG] GetGlyphBitmap: font=%s glyph=%d pixel_scale=%.3f truePixelScale=%.1f glyphScale=%.0f\n",
-				m_cFontData->getFontName().c_str(), glyph, pixel_scale, tps, glyphScale);
-		}
-	}
-
 	// 4J-JEV: Debug code to check which font sizes are being used.
 #if (!defined _CONTENT_PACKAGE) && (VERBOSE_FONT_OUTPUT > 0)