Summary:
Thanks to commit b263910ba90dd273d10a8ecffa90b8affcdea529, we can bring
back the ItemPointer static assert.  Follow the new code (see upstream
postgres 75f49221c22286104f032827359783aa5f4e6646).

Jira: DB-15331

Test Plan:
Close: #25997
Jenkins: compile only

Reviewers: amartsinchyk, aagrawal

Reviewed By: aagrawal

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D41853