fix(drag): continue autoscroll when widget dragged past root container edge

[developerVibhay]

Description

When a gridstack container is scrollable and you drag a widget aggressively toward the top of the browser window — pulling it fully above the container's visible area — autoscroll stops instead of continuing
to scroll up (or down when dragged below).

Root cause: _getClipping() in dd-draggable.ts had an early return for the "fully outside" case:

if (elRect.bottom < scrollRect.top || elRect.top > scrollRect.bottom) return 0;

This is correct for nested grid containers (the widget has left that grid, so the parent should take over). But when the scroll container is the document root, there is no parent to hand off to — scrolling
should continue at full speed.

Fix: Added an isRoot check so the early return only applies to nested containers:

const isRoot = scrollEl === (document.scrollingElement || document.documentElement);
if (!isRoot && (elRect.bottom < scrollRect.top || elRect.top > scrollRect.bottom)) return 0;

Example: Create a gridstack grid taller than the viewport (so the page scrolls). Grab the last widget and quickly drag it toward the top of the browser window past the visible area. Before this fix, autoscroll
would halt as soon as the widget left the visible bounds. After this fix, the container continues scrolling up until it reaches the top.

[adumesny]

shouldn't scrolling stop when we have nothing else to scroll instead of where item is relative to scrollRect ? I mean the original scrollElement shoud continue reguadless if we enter a parent grid or not. Also your check for main view but could be a regualr parent div that still above all grid, so your logic isn't matchign to wording anyway...

[adumesny]

see comment