[legacy] Restore old floating style inside Vector

This is a modified revert of Ia1eec412111e8f6af3b45affdc186d9eafd4262c.
This is not applied to modern Vector, for reasons given on ticket.

Change-Id: I3234e7712b8c111b070c35e38425c865ff7213f9

resources/skins.vector.styles/legacy/layout.less

@@ -61,6 +61,12 @@ body {
 	z-index: @z-index-base;
 }
 
+// FIXME: Can be removed when the `content-parser-output` feature in `skins.vector.styles.legacy`
+// is enabled. The definition in core still needs work (see T279008).
+#bodyContent {
+	.mixin-clearfix();
+}
+
 /* Head */
 #mw-page-base {
 	.vertical-gradient( @background-color-base, @background-color-secondary, 50%, 100% );

skin.json

@@ -99,6 +99,7 @@
 		"skins.vector.styles.legacy": {
 			"class": "ResourceLoaderSkinModule",
 			"features": {
+				"content-parser-output": false,
 				"normalize": true,
 				"elements": true,
 				"content": true,