[4.2] Move demo tasks to service provider

[laoneo]

Summary of Changes

Move the demo task plugin to service provider.

Testing Instructions

Create different demo tasks like the memory stress test or sleep.

Actual result BEFORE applying this Pull Request

All works.

Expected result AFTER applying this Pull Request

All works.

[alikon]

I have tested this item ✅ successfully on ee60281

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[heelc29]

I have tested this item ✅ successfully on ee60281

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[richard67]

RTC

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[richard67]

If this gets merged before 4.0.0-beta2, I will have to update the list of deleted files in script.php again. I would need to add file "/plugins/task/demotasks/demotasks.php" to the list of deleted files at line 6485.

I've prepared already a branch for that.

[alikon]

wait then ...
consider this too #38072

[richard67]

wait then ... consider this too #38072

@alikon Sure, when it has RTC I will add the "plugins/task/checkfiles/checkfiles.php" file, too.

[roland-d]

Thanks everybody