[pp-1] Use project objects directly rather than project names in checkProjects

Problem/Motivation

In #3037031: Convert locale.compare.inc to a service we cleaned up project comparison a lot, however there is more work to be done around checkProjects and checkLocalProjects

Postponed on: #3215707: [META] Modernize Locale module

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet