Shift thumbnail dislay to use object-fit to preserve aspect-ratio

res/css/views/messages/_MImageBody.scss

@@ -21,11 +21,7 @@ $timelineImageBorderRadius: 4px;
 }
 
 .mx_MImageBody_thumbnail {
-    position: absolute;
-    width: 100%;
-    height: 100%;
-    left: 0;
-    top: 0;
+    object-fit: contain;
     border-radius: $timelineImageBorderRadius;
 
     display: flex;

src/components/views/messages/MImageBody.tsx

@@ -362,7 +362,6 @@ export default class MImageBody extends React.Component<IBodyProps, IState> {
         const thumbnail = (
             <div className="mx_MImageBody_thumbnail_container" style={{ maxHeight: maxHeight + "px", maxWidth: maxWidth + "px" }} >
                 { /* Calculate aspect ratio, using %padding will size _container correctly */ }
-                <div style={{ paddingBottom: forcedHeight ? (forcedHeight + "px") : ((100 * infoHeight / infoWidth) + '%') }} />
                 { showPlaceholder &&
                     <div className="mx_MImageBody_thumbnail" style={{
                         // Constrain width here so that spinner appears central to the loaded thumbnail