Add property declarations for defined app modules

[gauthierm]

Description

Adds PHPstan property declarations for module definitions.

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[cviebrock]

Above, we set the type with a docblock comment. The worry I have with explicitly typing the property would be that we run into the "access before setting" issue ... in which case it needs to be nullable (and then we need to do null checks throughout the code).

Any concerns on your end?

[gauthierm]

I had that concern as well. I did test the cache table updater and it runs correctly. I think if we ever had a access before setting issue in the code, we'd also have a null-dereference issue as none of the code checks for null on this property.