(core) When managing focus, don't auto-scroll

Summary:
When Grist is embedded, calls to focus() cause the outer page to scroll to the embed iframe. Because this happens automatically on load, this cause the page to jump to the embed (not consistent across browsers, but at least in Chrome on Windows).

This change changes the automatic focus() calls to avoid scrolling. In the normal app, it should make no difference; in embedded context, this avoids the unexpected scrolling of the parent page.

Test Plan: Tested manually, with Anais's help: in her browser, embedded Grist consistently caused the page to jump to the embed before the change, and not after.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3631

app/client/lib/FocusLayer.ts

@@ -82,7 +82,7 @@ class FocusLayerManager extends Disposable {
     this._focusLayers.push(layer);
     // Move the focus to the new layer. Not just grabFocus, because if the focus is on the previous
     // layer's defaultFocusElem, the new layer might consider it "allowed" and never get the focus.
-    setTimeout(() => layer.defaultFocusElem.focus(), 0);
+    setTimeout(() => layer.defaultFocusElem.focus({preventScroll: true}), 0);
   }
 
   public removeLayer(layer: FocusLayer) {
@@ -121,7 +121,7 @@ class FocusLayerManager extends Disposable {
       watchElementForBlur(document.activeElement, () => this.grabFocus());
       layer.onDefaultBlur();
     } else {
-      layer.defaultFocusElem.focus();
+      layer.defaultFocusElem.focus({preventScroll: true});
       layer.onDefaultFocus();
     }
   }