API Don't publicly expose extension hook methods

[GuySartorelli]

Extension hook methods should be protected - this should be best practices for CMS 5 now that it is a possibility as it reduces the public API surface extensions introduce.

Parent Issue

• Make extension hook methods protected #10514

[emteknetnz]

This is something that definitely requires a level of automated code scanning, it's simply too error prone to do this manually

Will create the PRs using https://github.com/emteknetnz/extension-protector/