Convert user page extensions to D10

Problem/Motivation

In earlier versions, G2 used to provide a listing of the G2 entries most recently created by the user.

This was implemented by the relatively inefficient process of loading those nodes on hook_user_load, which is invoked in many cases beyond the user profile page. It needs to be converted to a more efficient service-based lazy process.

Steps to reproduce

• create a published G2 entry
• navigate to /user
• observe the node being listed: currently not there but it should be, either always or by configuring a block for it.

Proposed resolution

Replace the hook_user_load mechanism by something triggered only on the user.page route.

Remaining tasks

• Decide on the details of implementation: likely service, block plugin, default block, view...
• Implement.

User interface changes

None planned.

API changes

None.

Data model changes

None.