Cherry-pick 7fc4f61. rdar://problem/111697949

    REGRESSION(265615@main): <attachment> icon is stretched
    https://bugs.webkit.org/show_bug.cgi?id=258832
    rdar://111697949

    Reviewed by Wenson Hsieh.

    Using <img> by default will stretch the icon, adding `object-fit: contain` makes sure the original image aspect ratio is honored, restoring the old behavior.

    * Source/WebCore/html/shadow/attachmentElementShadow.css:
    (img#attachment-icon):

    Canonical link: https://commits.webkit.org/265742@main

Identifier: 265693.3@safari-7616.1.22-branch

Source/WebCore/html/shadow/attachmentElementShadow.css

@@ -73,6 +73,7 @@ img#attachment-icon {
     width: 52px;
     height: 52px;
 #endif
+    object-fit: contain;
     overflow: hidden;
 }