Convert test_DateTextBox.html to AMD, refs #18394.

(cherry picked from commit 202d9e6e4de1b7a11a527ee100ca35ef3b94e029)
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()`).

(cherry picked from commit c6d9f7bb6578fc6e22a19fc1175e24094a39ebb9)