[Fix] Gradient Text Support

Runtime/painting/text_style.cs

             this.fontFamily = fontFamily;
             this._fontFamilyFallback = fontFamilyFallback;
             this.debugLabel = debugLabel;
+            this.foreground = foreground;
             this.background = background;
         }
 
                 decorationColor: decorationColor ?? this.decorationColor,
                 decorationStyle: decorationStyle ?? this.decorationStyle,
                 decorationThickness: decorationThickness ?? this.decorationThickness,
+                foreground: foreground ?? this.foreground,
                 background: background ?? this.background,
                 debugLabel: newDebugLabel
             );

Runtime/ui/text.cs

         public readonly Color decorationColor;
         public readonly TextDecorationStyle decorationStyle = kDefaultDecorationStyle;
         public readonly string fontFamily = kDefaultFontFamily;
+        public readonly Paint foreground;
         public readonly Paint background;
 
         internal UnityEngine.Color UnityColor {
                     decoration: style.decoration ?? currentStyle.decoration,
                     decorationColor: style.decorationColor ?? currentStyle.decorationColor,
                     fontFamily: style.fontFamily ?? currentStyle.fontFamily,
+                    foreground: style.foreground ?? currentStyle.foreground,
                     background: style.background ?? currentStyle.background
                 );
             }
                 decoration: style.decoration,
                 decorationColor: style.decorationColor,
                 fontFamily: style.fontFamily,
+                foreground: style.foreground,
                 background: style.background
             );
         }
             float? wordSpacing = null, TextBaseline? textBaseline = null, float? height = null,
             TextDecoration decoration = null, TextDecorationStyle? decorationStyle = null, Color decorationColor = null,
             string fontFamily = null,
+            Paint foreground = null,
             Paint background = null
         ) {
             this.color = color ?? this.color;
             this.decorationStyle = decorationStyle ?? this.decorationStyle;
             this.decorationColor = decorationColor ?? this.decorationColor;
             this.fontFamily = fontFamily ?? this.fontFamily;
+            this.foreground = foreground ?? this.foreground;
             this.background = background ?? this.background;
         }
     }

Runtime/ui/txt/paragraph.cs

             this._paragraphStyle = null;
         }
 
-        readonly Paint _textPaint = new Paint {
+        Paint _textPaint = new Paint {
             filterMode = FilterMode.Bilinear
         };
 
 
             for (int i = 0; i < this._paintRecordsCount; i++) {
                 var paintRecord = this._paintRecords[i];
-                this._textPaint.color = paintRecord.style.color;
+                
+                if (paintRecord.style.foreground != null) {
+                    this._textPaint = paintRecord.style.foreground;
+                } else {
+                    this._textPaint.color = paintRecord.style.color;
+                }
+
+                
                 this.paintDecorations(canvas, paintRecord, offset);
             }
         }