fix(Icon): update typings for corner prop (#3393)

* Corner prop can be a string, not just boolean

See docs: https://react.semantic-ui.com/elements/icon/

* Update Icon.d.ts

src/elements/Icon/Icon.d.ts

@@ -4,6 +4,7 @@ import { SemanticCOLORS, SemanticICONS } from '../../generic'
 import IconGroup from './IconGroup'
 
 export type IconSizeProp = 'mini' | 'tiny' | 'small' | 'large' | 'big' | 'huge' | 'massive'
+export type IconCorner = 'bottom right' | 'top right' | 'top left' | 'bottom left'
 
 export interface IconProps extends StrictIconProps {
   [key: string]: any
@@ -26,7 +27,7 @@ export interface StrictIconProps {
   color?: SemanticCOLORS
 
   /** Icons can display a smaller corner icon. */
-  corner?: boolean
+  corner?: boolean | IconCorner
 
   /** Show that the icon is inactive. */
   disabled?: boolean