Fix DataLoader inspection and re-instantiation in Lite

[awaelchli]

What does this PR do?

Part of #10329

A detailed explanation of why the bug occurs can be found in the linked issue.
A newly added test demonstrates the failure on master.

This fix should be reviewed carefully, at least by @carmocca and @tchaton .

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Did you have fun?

I made sure I had fun coding 🙃

Part of #1 (it's a lie, this is just here to avoid noisy GitHub bot)

[tchaton]

@carmocca Do you think we should bring this to Lightning too ?

[carmocca]

LGTM

[awaelchli]

Is it the approach of how we handle dataloaders in general or the fix that I added?