feat(webgl): Add WEBGL_GAL implementation (compiles, not yet rendering)

Copy and adapt OpenGL GAL to WebGL:
- Copy all OpenGL GAL source files to tests/gal-regression/wasm/webgl/
- Rename classes from OPENGL_* to WEBGL_*
- Add kiglew.h with WebGL2/GLES3 headers and GLEW stubs
- Add webgl_antialiasing.h/cpp adapted for WEBGL_COMPOSITOR
- Add shader generator (generate_shaders.py) for WASM build
- Update Makefile with all KiCad dependencies (C++20, GLM, clipper2, etc.)

Build produces 544KB JS + 4.9MB WASM. Tests run but render blank
(expected - GL context initialization needs WebGL adaptation).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/gal-regression/wasm/webgl/gl_resources.cpp

@@ -0,0 +1,63 @@
+/*
+* This program source code file is part of KICAD, a free EDA CAD application.
+*
+* Copyright The KiCad Developers, see AUTHORS.txt for contributors.
+*
+* This program is free software; you can redistribute it and/or
+* modify it under the terms of the GNU General Public License
+* as published by the Free Software Foundation; either version 2
+* of the License, or (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program; if not, you may find one here:
+* http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+* or you may search the http://www.gnu.org website for the version 2 license,
+* or you may write to the Free Software Foundation, Inc.,
+* 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+*/
+
+// The current font is "Ubuntu Mono" available under Ubuntu Font Licence 1.0
+// (see ubuntu-font-licence-1.0.txt for details)
+#include <algorithm>
+#include "gl_resources.h"
+
+#define BITMAP_FONT_USE_SPANS
+
+namespace KIGFX {
+namespace BUILTIN_FONT {
+
+#include "bitmap_font_img.c"
+#include "bitmap_font_desc.c"
+
+const FONT_GLYPH_TYPE* LookupGlyph( unsigned int aCodepoint )
+{
+#ifdef BITMAP_FONT_USE_SPANS
+    auto *end = font_codepoint_spans + sizeof( font_codepoint_spans ) / sizeof(FONT_SPAN_TYPE);
+
+    auto ptr = std::upper_bound( font_codepoint_spans, end, aCodepoint,
+            []( unsigned int codepoint, const FONT_SPAN_TYPE& span )
+            {
+                return codepoint < span.end;
+            } );
+
+    if( ptr != end && ptr->start <= aCodepoint )
+    {
+        unsigned int index = aCodepoint - ptr->start + ptr->cumulative;
+        return &font_codepoint_infos[ index ];
+    }
+    else
+    {
+        return nullptr;
+    }
+#else
+    return &bitmap_chars[codepoint];
+#endif
+}
+
+}
+}