Fix autocompletion on ::create and ::strong_create

Currently `::create` and `::strong_create` are documented as returning `Object`. This breaks autocompletion for IDEs as they assume `Object` is being returned, when in actual fact a subclass is. `@return static` will make the IDE assume the LSB class is being returned. This will *greatly* help working in IDEs and avoid having to use `/** @var SomeObject $obj */` all the time.

Obviously this won't always be the case due to `::useCustomClass`, however that's an exception to the rule and still doesn't break anything code-wise.