Update wc_get_page_id compatability return type

[johnolek]

What?

This updates the compatibility version of wc_get_page_id to always return an integer to match the behavior of WC core. The current behavior of returning a string could cause issues with themes/plugins that are expecting an integer value.

Tickets / Documentation

• Current definition of wc_get_page_id

[karmatosed]

This looks like it doesn't have any conflicts with the current branch, but it would be great to work out how to move it on from sitting. Would it be able to get a review @chanceaclark?

[bc-erich]

@chanceaclark What is the merge process? Can we merge this or does the contributor merge this? We should document the merge process for future reference