[CrOS Wallpaper] Place spinner in correct location for RTL languages.

The spinner is currently placed in the LTR location for RTL languages.
This CL places the spinner in the correct location for either.

Bug: 918122
Change-Id: Ie264f0b8e967fdf8abe04573a08c270a32dbc425
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1888777Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710912}

chrome/browser/resources/chromeos/wallpaper_manager/css/wallpaper_manager.css

@@ -870,7 +870,7 @@ html[dir='rtl'] .top-header-contents .more-options {
 
 #current-wallpaper-spinner {
   height: 24px;
-  left: 38px;
+  margin-inline-start: 38px;
   top: 38px;
   width: 24px;
 }