[Feature] support background config in the text of richtext

[xiaoluoHe]

What problem does this feature solve?

富文本中文字支持背景相关配置，包括: background,backgroundOpacity,backgroundCornerRadius

What does the proposed API look like?

export type IRichTextParagraphCharacter = IRichTextBasicCharacter & {
 ...
  // Add these attributes:
  backgroundShowMode?: 'always' | 'hover' | 'never';
  backgroundFill?: boolean | IColor; // 背景矩形填充颜色
  backgroundFillOpacity?: number; // 背景矩形填充透明度
  backgroundStroke?: boolean | IColor; // 背景矩形边框颜色
  backgroundStrokeOpacity?: number; // 背景矩形边框透明度
  backgroundRadius?: number; // 背景矩形圆角
  backgroundWidth?: number;
  backgroundHeight?: number;
};