fix types (#9242)

overload validate method
add clearValidate method

types/form.d.ts

@@ -57,8 +57,8 @@ export declare class ElForm extends ElementUIComponent {
    *
    * @param callback A callback to tell the validation result
    */
-  validate (callback?: ValidateCallback): any
-
+  validate (callback: ValidateCallback): void
+  validate (): Promise<boolean>
   /**
    * Validate a certain form item
    *
@@ -69,4 +69,7 @@ export declare class ElForm extends ElementUIComponent {
 
   /** reset all the fields and remove validation result */
   resetFields (): void
+  
+  /** clear validation message for all fields */
+  clearValidate (): void
 }