[feature] Add trailing option

[wcoder]

Add leading/trailing options to RichText.

Use case:

• Display required string should display with an asterisk, example: Name*

Solution:

Add:

		
final TextSpan trailing;

// ...

		if (trailing != null) {
          children.add(trailing);
        }

		// end
        return Text.rich(TextSpan(children: children));

Usage:

RichText(
  text: 'Name',
  trailing: TextSpan(
  	text: '*',
  	//style: can be red color
  ),
),

[remoteportal]

released in version 2.0.47 (2021-05-22)