refs #14498 - do not create global static instances of the checks

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Since we switched to non-OBJECT library everything which links against lib will instantiate all checks even if never used (i.e. dmake). This changes the code only instantiate them if they are actually requested.

As a follow-up we can stop relying on the global check instances in the tests and use local ones instead. As a final step this will (hopefully) finally allow us to land #5323.

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As another positive side effect this no longer needs to return a mutable reference.

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As we now have a fixed order of the checks there no longer is any reason to sort them.

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Maybe someone can come up with an improved macro that would also build the list so we only need to specify the check name once. Could also be done in a follow-up since I have other changes already lined up.

[danmar]

Alright. I wanted from the start that checks are dynamic so it would be possible to link extra checker classes dynamically. I.e. users could develop custom checkers.
But checkers will never be linked dynamically in that way so we can as well do this.

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Alright. I wanted from the start that checks are dynamic so it would be possible to link extra checker classes dynamically. I.e. users could develop custom checkers. But checkers will never be linked dynamically in that way so we can as well do this.

I think that plan was superseded by the addons. Even if that functionality would be added those can still be dynamically added to the list - should be even more possible then before when the object creation wasn't controlled.