DatePicker: Fix flatpickrWrapper is not defined error

[panmona]

First of all thanks for maintaining this library!

When updating from Blazorise 1.3.3 to the newest 1.4.3, we started to notice the following error logs in the console:

datePicker.js?v=1.4.3.0:118 Uncaught ReferenceError: flatpickrWrapper is not defined
    at ClassWatcher.successClassAddHandler [as classAddedCallback] (datePicker.js?v=1.4.3.0:118:17)
    at MutationObserver.mutationCallback (observer.js?v=1.4.3.0:90:30)

The component behavior seems to still be as excepted though.

I suspect that this is because in #5093 the successClassAddHandler functions were moved outside of the scope where the flatpickrWrapper is available. In the PR I unfortunately wasn't able to see why this was changed. The PR seems to me a bit unrelated to those functions.
I'm very open to change the PR if my analysis was incorrect!

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[panmona]

I have read the CLA Document and I hereby sign the CLA

[stsrki]

LGTM.

Not sure how we missed that as it seems pretty obvious not to be placed there.

Thank you for the contribution!