fix: Form and Mention TypeScript definition (#6268)

* Add source and options params to Form.ValidationRule.validator function

As per rules section of async-validation readme: https://github.com/yiminghe/async-validator#rules

* Make prefixCls optional in MentionProps interface

components/form/Form.tsx

@@ -52,7 +52,7 @@ export type ValidationRule = {
   /** transform a value before validation */
   transform?: (value: any) => any;
   /** custom validate function (Note: callback must be called) */
-  validator?: (rule: any, value: any, callback: any) => any;
+  validator?: (rule: any, value: any, callback: any, source?: any, options?: any) => any;
 };
 
 export type ValidateCallback = (erros: any, values: any) => void;

components/mention/index.tsx

@@ -5,7 +5,7 @@ import shallowequal from 'shallowequal';
 import Icon from '../icon';
 
 export interface MentionProps {
-  prefixCls: string;
+  prefixCls?: string;
   suggestionStyle?: React.CSSProperties;
   suggestions?: Array<any>;
   onSearchChange?: Function;