LibGfx+LibWeb: Update definitions of supported font formats and features

Based very scientifically on what's listed here:
https://harfbuzz.github.io/what-does-harfbuzz-do.html

I've moved the code into LibGfx because including a HarfBuzz header
directly from LibWeb is a little unpleasant. But the Gfx::FontTech enum
follows the CSS definitions for font features for simplicity.

TrueType collections are supported. SVG and Embedded OpenType are not,
but they're not widely supported by other browsers so that's fine.

Most of the features are completely supported by HarfBuzz, so we can
just return true. Graphite support is optional (and it appears we use a
build of HarfBuzz without it) but there's a define we can check.
Incremental Font Transfer is a whole separate thing that we definitely
don't support yet.

Libraries/LibGfx/CMakeLists.txt

@@ -14,6 +14,7 @@ set(SOURCES
     Font/Font.cpp
     Font/FontData.cpp
     Font/FontDatabase.cpp
+    Font/FontSupport.cpp
     Font/PathFontProvider.cpp
     Font/Typeface.cpp
     Font/TypefaceSkia.cpp

Libraries/LibGfx/Font/FontSupport.cpp

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGfx/Font/FontSupport.h>
+
+#include <harfbuzz/hb.h>
+
+namespace Gfx {
+
+bool font_format_is_supported(FontFormat const format)
+{
+    // FIXME: Determine these automatically.
+    switch (format) {
+    case FontFormat::EmbeddedOpenType:
+        return false;
+    case FontFormat::OpenType:
+        return true;
+    case FontFormat::SVG:
+        return false;
+    case FontFormat::TrueType:
+        return true;
+    case FontFormat::TrueTypeCollection:
+        return true;
+    case FontFormat::WOFF:
+        return true;
+    case FontFormat::WOFF2:
+        return true;
+    }
+
+    return false;
+}
+
+bool font_tech_is_supported(FontTech const font_tech)
+{
+    // https://drafts.csswg.org/css-fonts-4/#font-tech-definitions
+    // FIXME: Determine these automatically.
+    switch (font_tech) {
+    case FontTech::FeaturesOpentype:
+        // GSUB and GPOS, supported by HarfBuzz
+        return true;
+    case FontTech::FeaturesAat:
+        // morx and kerx, supported by HarfBuzz
+        return true;
+    case FontTech::FeaturesGraphite:
+        // Silf, Glat , Gloc , Feat and Sill. HarfBuzz may or may not be built with support for it.
+#if HB_HAS_GRAPHITE
+        return true;
+#else
+        return false;
+#endif
+    case FontTech::Variations:
+        // avar, cvar, fvar, gvar, HVAR, MVAR, STAT, and VVAR, supported by HarfBuzz
+        return true;
+    case FontTech::ColorColrv0:
+    case FontTech::ColorColrv1:
+        // COLR, supported by HarfBuzz
+        return true;
+    case FontTech::ColorSvg:
+        // SVG, supported by HarfBuzz
+        return true;
+    case FontTech::ColorSbix:
+        // sbix, supported by HarfBuzz
+        return true;
+    case FontTech::ColorCbdt:
+        // CBDT, supported by HarfBuzz
+        return true;
+    case FontTech::Palettes:
+        // CPAL, supported by HarfBuzz
+        return true;
+    case FontTech::Incremental:
+        // Incremental Font Transfer: https://w3c.github.io/IFT/Overview.html
+        return false;
+    // https://drafts.csswg.org/css-fonts-5/#font-tech-definitions
+    case FontTech::Avar2:
+        // avar version 2, supported by HarfBuzz
+        return true;
+    }
+    return false;
+}
+
+}

Libraries/LibGfx/Font/FontSupport.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Types.h>
+
+namespace Gfx {
+
+enum class FontFormat : u8 {
+    EmbeddedOpenType,
+    OpenType,
+    SVG,
+    TrueType,
+    TrueTypeCollection,
+    WOFF,
+    WOFF2,
+};
+
+enum class FontTech : u8 {
+    Avar2,
+    ColorCbdt,
+    ColorColrv0,
+    ColorColrv1,
+    ColorSbix,
+    ColorSvg,
+    FeaturesAat,
+    FeaturesGraphite,
+    FeaturesOpentype,
+    Incremental,
+    Palettes,
+    Variations,
+};
+
+bool font_format_is_supported(FontFormat);
+bool font_tech_is_supported(FontTech);
+
+}