Convert test_DateTextBox.html to AMD, refs #18394.
When dateClassObj is not the native javascript Date object,
make sure that this.value is always a dateClassObj.

Fixes #18394, a problem with hebrew calendars.

Unfortunately I don't have an automated test case since it requires code
in dojox/date to test.

Refs #5074 (the support for specifying non-gregorian calendars),
and refs #11251 (which is when the custom `_set()` method was added that calls `compare()`).
Don't expand a tree node when dropping below the node
(i.e. dropping between a collapsed node and its next sibling).

Fixes #17977.