fix(drag-drop): error when dragging items inside transplanted… (#18356)

This is a bit of an edge case, but nevertheless it's something that can happen. The way the dragging sequence works is that the drop list keeps track of its items via `ContentChildren` and it registers itself with them once they're picked up by the `QueryList`. If an item doesn't have a container when the drag sequence is started, it is considered a "standalone" drag.

This becomes a problem with transplanted views (e.g. ones created by `cdk-table`) that use OnPush where we could end up in a situation where the items aren't picked up during the first pass, but when the user starts dragging, we trigger change detection and the `QueryList` is updated, but at that point it's too late, because we've already started the dragging sequence with a different set of information.

These changes work around the issue by assigning the container manually again through the drag directive.

A couple of notes:
* This is a second iteration of the fix. I went with this approach, because it doesn't require hacky timeouts and triggering change detection again. See the origin approach here: 22afc37
* It's difficult to capture this in a test, because we'd have to duplicate half of the logic from `CdkTable` and we might still not be able to get the same change detection timing due to `TestBed`.

Fixes #18341.

Author: crisbeto

src/cdk/drag-drop/directives/drag.ts

@@ -206,6 +206,17 @@ export class CdkDrag<T = any> implements AfterViewInit, OnChanges, OnDestroy {
       this._assignDefaults(config);
     }
 
+    // Note that usually the container is assigned when the drop list is picks up the item, but in
+    // some cases (mainly transplanted views with OnPush, see #18341) we may end up in a situation
+    // where there are no items on the first change detection pass, but the items get picked up as
+    // soon as the user triggers another pass by dragging. This is a problem, because the item would
+    // have to switch from standalone mode to drag mode in the middle of the dragging sequence which
+    // is too late since the two modes save different kinds of information. We work around it by
+    // assigning the drop container both from here and the list.
+    if (dropContainer) {
+      this._dragRef._withDropContainer(dropContainer._dropListRef);
+    }
+
     this._syncInputs(this._dragRef);
     this._handleEvents(this._dragRef);
   }