Center dropdown toggle correctly across browsers (#5395)

This commit also fixes the shifting issue for Firefox when the dropdown
toggle is clicked.

browser/app/less/inc/file-explorer.less

@@ -62,7 +62,7 @@
 			background: darken(@red, 10%);
 
 			& > span {
-				.rotate(135deg);
+				transform: translateZ(1px) rotate(135deg);
 			}
 		}
 	}
@@ -89,7 +89,7 @@
 	i {
 		color: @white;
 		font-size: 17px;
-		line-height: 58px;
+		line-height: 55px;
 	}
 }
 

browser/yarn.lock

@@ -2894,6 +2894,10 @@ macaddress@^0.2.8:
   version "0.2.8"
   resolved "https://registry.yarnpkg.com/macaddress/-/macaddress-0.2.8.tgz#5904dc537c39ec6dbefeae902327135fa8511f12"
 
+material-design-iconic-font@^2.2.0:
+  version "2.2.0"
+  resolved "https://registry.yarnpkg.com/material-design-iconic-font/-/material-design-iconic-font-2.2.0.tgz#66c3b1c880ef0cb87c02ca2a0f900ff0fe7f480d"
+
 math-expression-evaluator@^1.2.14:
   version "1.2.17"
   resolved "https://registry.yarnpkg.com/math-expression-evaluator/-/math-expression-evaluator-1.2.17.tgz#de819fdbcd84dccd8fae59c6aeb79615b9d266ac"