set max tree width to 1200px (apache#16067)

the totalwidth of the tree view will depend on the window size like before, but max out at 1200px

(cherry picked from commit f2aa9b5)
(cherry picked from commit eefa563)

airflow/www/static/js/tree.js

@@ -70,7 +70,9 @@ document.addEventListener('DOMContentLoaded', () => {
     if (node.depth > treeDepth) treeDepth = node.depth;
   });
   treeDepth += 1;
-  const squareX = window.innerWidth - (data.instances.length * squareSize) - (treeDepth * 50);
+
+  const innerWidth = window.innerWidth > 1200 ? 1200 : window.innerWidth;
+  const squareX = innerWidth - (data.instances.length * squareSize) - (treeDepth * 50);
 
   const squareSpacing = 2;
   const margin = {