[MM-56292] Convert ./components/widgets/icons/checkbox_partial_icon.tsx from Class Component to Function Component (#25764)

* [MM-56292] Convert `./components/widgets/icons/checkbox_partial_icon.tsx` from Class Component to Function Component

* refactor: update snapshots

webapp/channels/src/components/admin_console/permission_schemes_settings/__snapshots__/permission_checkbox.test.tsx.snap

@@ -37,6 +37,6 @@ exports[`components/admin_console/permission_schemes_settings/permission_checkbo
   className="permission-check intermediate"
   data-testid="uniqId-checked"
 >
-  <CheckboxPartialIcon />
+  <Memo(CheckboxPartialIcon) />
 </div>
 `;

webapp/channels/src/components/widgets/icons/checkbox_partial_icon.tsx

@@ -1,11 +1,9 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import React from 'react';
+import React, {memo} from 'react';
 
-export default class CheckboxPartialIcon extends React.PureComponent {
-    render() {
-        return (
+const CheckboxPartialIcon = () => (
     <svg
         width='18px'
         height='18px'
@@ -57,6 +55,6 @@ export default class CheckboxPartialIcon extends React.PureComponent {
             </g>
         </g>
     </svg>
-        );
-    }
-}
+);
+
+export default memo(CheckboxPartialIcon);