CM6: ensure search panel is in the same direction as the interface lang

We don't have access to the HTML attributes for .cm-panels, so we just
use CSS to set the direction.

Bug: T359611
Change-Id: I1d40ae4f7dc093f585051d388c70cde151faa5e6

src/codemirror.js

@@ -164,6 +164,12 @@ class CodeMirror {
 				// These should be attributes of .cm-editor, not the .cm-content (T359589)
 				dir: this.$textarea.attr( 'dir' ),
 				lang: this.$textarea.attr( 'lang' )
+			} ),
+			// The search panel should use the same direction as the interface langauge (T359611)
+			EditorView.theme( {
+				'.cm-panels': {
+					direction: document.dir
+				}
 			} )
 		];
 	}