Make usePage a generic

[lepikhinb]

The fix brings a generic to the usePage method.

Example usage:

const props = usePage<{ notification?: string }>().props;

const notification = props.notification;

[jessarcher]

Thank you! I ended up going with #1394, which solves the same problem.

[lepikhinb]

@jessarcher somehow, I missed your PR when I was looking for a similar one. Thanks!