Keep current cursor or top line in view when resizing Console to avoi…

…d losing user context (elastic#13695)

* keep current cursor or top line in view when resizing to avoid losing user context

* rename variable to more descriptive name

* move state from editor to smart_resize

src/core_plugins/console/public/src/input_resize.js

@@ -24,6 +24,8 @@ module.exports = function (input, output) {
       $resizer.addClass('active');
       var startWidth = $left.width();
       var startX = event.pageX;
+      input.resize.topRow = input.renderer.layerConfig.firstRow;
+      output.resize.topRow = output.renderer.layerConfig.firstRow;
 
       function onMove(event) {
         setEditorWidth(startWidth + event.pageX - startX)

src/core_plugins/console/public/src/smart_resize.js

@@ -1,6 +1,16 @@
-import { throttle } from 'lodash';
+import { get, throttle } from 'lodash';
 
 module.exports = function (editor) {
   const resize = editor.resize;
-  return throttle(() => resize.call(editor), 35)
-};
+  const throttledResize = throttle(() => {
+
+    resize.call(editor);
+
+    // Keep current top line in view when resizing to avoid losing user context
+    let userRow = get(throttledResize, 'topRow', 0);
+    if (userRow !== 0) {
+      editor.renderer.scrollToLine(userRow, false, false, () => {});
+    }
+  }, 35);
+  return throttledResize;
+}