feat(Tag): add prop effect. (#15725)

types/tag.d.ts

@@ -1,10 +1,11 @@
 import { ElementUIComponent, ElementUIComponentSize } from './component'
 
 export type TagType = 'primary' | 'gray' | 'success' | 'warning' | 'danger'
+export type TagTheme = 'dark' | 'light' | 'plain'
 
 /** Tag Component */
 export declare class ElTag extends ElementUIComponent {
-  /** Theme */
+  /** Tag type */
   type: TagType
 
   /** Whether Tab can be removed */
@@ -21,4 +22,7 @@ export declare class ElTag extends ElementUIComponent {
 
   /** Tag size */
   size: ElementUIComponentSize
+
+  /** Tag theme */
+  effect: TagTheme
 }