Simulate font weight bold and font style italic when a fallback is used

src/Skia/Avalonia.Skia/FontManagerImpl.cs

@@ -140,7 +140,11 @@ namespace Avalonia.Skia
                     $"Could not create glyph typeface for: {typeface.FontFamily.Name}.");
             }
 
-            return new GlyphTypefaceImpl(skTypeface);
+            var isFakeBold = (int)typeface.Weight >= 600 && !skTypeface.IsBold;
+
+            var isFakeItalic = typeface.Style == FontStyle.Italic && !skTypeface.IsItalic;
+            
+            return new GlyphTypefaceImpl(skTypeface, isFakeBold, isFakeItalic);
         }
     }
 }

src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Skia
     {
         private bool _isDisposed;
 
-        public GlyphTypefaceImpl(SKTypeface typeface)
+        public GlyphTypefaceImpl(SKTypeface typeface, bool isFakeBold = false, bool isFakeItalic = false)
         {
             Typeface = typeface ?? throw new ArgumentNullException(nameof(typeface));
 
@@ -52,6 +52,10 @@ namespace Avalonia.Skia
                 0;
 
             IsFixedPitch = Typeface.IsFixedPitch;
+
+            IsFakeBold = isFakeBold;
+
+            IsFakeItalic = isFakeItalic;
         }
 
         public Face Face { get; }
@@ -86,6 +90,10 @@ namespace Avalonia.Skia
 
         /// <inheritdoc cref="IGlyphTypefaceImpl"/>
         public bool IsFixedPitch { get; }
+        
+        public bool IsFakeBold { get; }
+        
+        public bool IsFakeItalic { get; }
 
         /// <inheritdoc cref="IGlyphTypefaceImpl"/>
         public ushort GetGlyph(uint codepoint)

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -217,6 +217,8 @@ namespace Avalonia.Skia
 
             s_font.Size = (float)glyphRun.FontRenderingEmSize;
             s_font.Typeface = typeface;
+            s_font.Embolden = glyphTypeface.IsFakeBold;
+            s_font.SkewX = glyphTypeface.IsFakeItalic ? -0.2f : 0;
 
 
             SKTextBlob textBlob;