Diff file tree tweaks (#21446)

- Left-align the diff stat line again like previously.
- Default the file tree to collapsed view, which means the tree will
rendered initially collapsed and it may "pop in" via JS if enabled. I
think this is more desirable than having the empty space for the tree
"pop out" like it currently does.
- Mute the icon, removing color unless hovered.
- Increase icon size and vertically center it.

Before:
<img width="1271" alt="image"
src="https://user-images.githubusercontent.com/115237/195666451-55771595-0525-42b8-be1b-d03cc1cb2961.png">


After:
<img width="1280" alt="image"
src="https://user-images.githubusercontent.com/115237/195666385-c91fd0de-6dcc-4d9c-89ff-7581828fcf14.png">

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/diff/box.tmpl

@@ -14,14 +14,16 @@
 {{else}}
 	<div>
 		<div class="diff-detail-box diff-box sticky df sb ac fw">
-			<a class="diff-toggle-file-tree-button">
+			<div class="df ac fw">
+				<a class="diff-toggle-file-tree-button muted df ac">
 					{{/* the icon meaning is reversed here, "octicon-sidebar-collapse" means show the file tree */}}
-				{{svg "octicon-sidebar-collapse" 16 "icon hide"}}
+					{{svg "octicon-sidebar-collapse" 20 "icon hide"}}
-				{{svg "octicon-sidebar-expand" 16 "icon"}}
+					{{svg "octicon-sidebar-expand" 20 "icon"}}
 				</a>
-			<div class="diff-detail-stats df ac">
+				<div class="diff-detail-stats df ac ml-3">
 					{{svg "octicon-diff" 16 "mr-2"}}{{.locale.Tr "repo.diff.stats_desc" .Diff.NumFiles .Diff.TotalAddition .Diff.TotalDeletion | Str2html}}
 				</div>
+			</div>
 			<div class="diff-detail-actions df ac">
 				{{if and .PageIsPullFiles $.SignedUserID (not .IsArchived)}}
 					<progress id="viewed-files-summary" class="mr-2" value="{{.Diff.NumViewedFiles}}" max="{{.Diff.NumFiles}}"></progress>
@@ -65,7 +67,7 @@
 				</script>
 		<div id="diff-file-list"></div>
 		<div id="diff-container">
-				<div id="diff-file-tree"></div>
+				<div id="diff-file-tree" class="hide"></div>
 				<div id="diff-file-boxes" class="sixteen wide column">
 					{{range $i, $file := .Diff.Files}}
 						{{/*notice: the index of Diff.Files should not be used for element ID, because the index will be restarted from 0 when doing load-more for PRs with a lot of files*/}}

web_src/less/_repository.less

@@ -3099,11 +3099,11 @@ td.blob-excerpt {
 
 @media @mediaMdAndDown {
   #diff-file-tree {
-    display: none;
+    display: none !important;
   }
 
   .diff-toggle-file-tree-button {
-    display: none;
+    display: none !important;
   }
 }