[MM-56298] Convert ./components/file_attachment/file_thumbnail/file_thumbnail.tsx from Class Component to Function Component (#25761)

* [MM-56298] Convert `./components/file_attachment/file_thumbnail/file_thumbnail.tsx` from Class Component to Function Component

* refactor: implement code review changes

webapp/channels/src/components/file_attachment/__snapshots__/file_attachment.test.tsx.snap

@@ -10,7 +10,7 @@ exports[`FileAttachment should match snapshot, after change from file to image 1
     href="#"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -99,7 +99,7 @@ exports[`FileAttachment should match snapshot, regular file 1`] = `
     href="#"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -332,7 +332,7 @@ exports[`FileAttachment should match snapshot, svg image 1`] = `
     href="#"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -532,7 +532,7 @@ exports[`FileAttachment should match snapshot, without compact display and witho
     href="#"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,

webapp/channels/src/components/file_attachment/file_thumbnail/file_thumbnail.tsx

@@ -1,7 +1,7 @@
 // Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
 // See LICENSE.txt for license information.
 
-import React from 'react';
+import React, {memo} from 'react';
 
 import type {FileInfo} from '@mattermost/types/files';
 
@@ -19,12 +19,12 @@ type Props = {
     fileInfo: FileInfo;
 }
 
-export default class FileThumbnail extends React.PureComponent<Props> {
-    render() {
-        const {fileInfo} = this.props;
+const FileThumbnail = ({
+    fileInfo,
+    enableSVGs,
+}: Props) => {
     const type = getFileType(fileInfo.extension);
 
-        let thumbnail;
     if (type === FileTypes.IMAGE) {
         let className = 'post-image';
 
@@ -48,18 +48,17 @@ export default class FileThumbnail extends React.PureComponent<Props> {
                 }}
             />
         );
-        } else if (fileInfo.extension === FileTypes.SVG && this.props.enableSVGs) {
-            thumbnail = (
+    } else if (fileInfo.extension === FileTypes.SVG && enableSVGs) {
+        return (
             <img
                 alt={'file thumbnail image'}
                 className='post-image normal'
                 src={getFileUrl(fileInfo.id)}
             />
         );
-        } else {
-            thumbnail = <div className={'file-icon ' + getIconClassName(type)}/>;
     }
 
-        return thumbnail;
-    }
-}
+    return <div className={'file-icon ' + getIconClassName(type)}/>;
+};
+
+export default memo(FileThumbnail);

webapp/channels/src/components/file_search_results/__snapshots__/file_search_result_item.test.tsx.snap

@@ -9,7 +9,7 @@ exports[`components/file_search_result/FileSearchResultItem should match snapsho
     className="FileSearchResultItem"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -167,7 +167,7 @@ exports[`components/file_search_result/FileSearchResultItem should match snapsho
     className="FileSearchResultItem"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -334,7 +334,7 @@ exports[`components/file_search_result/FileSearchResultItem should match snapsho
     className="FileSearchResultItem"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,
@@ -501,7 +501,7 @@ exports[`components/file_search_result/FileSearchResultItem should match snapsho
     className="FileSearchResultItem"
     onClick={[Function]}
   >
-    <Connect(FileThumbnail)
+    <Connect(Component)
       fileInfo={
         Object {
           "archived": false,