www/node16: copy from www/node, update 16.11.1 -> 16.12.0

Create a new port for the latest Node.js v16.x release, which will
become the v16.x LTS release line. Update CONFLICTS for the existing
Node.js ports to include the new node16 port and remove non-existent ports.

https://nodejs.org/en/blog/release/v16.12.0/

MFH: 2021Q4
Sponsored by: Miles AS