Move _title and _title_callback out of defaults section in existing route attributes

Problem/Motivation

Postponed on #3607968: Promote defaults._title to top level in route attributes

Need to include routes already converted in these issues:

• #3584823: Convert system module routes to use attributes
• #3585079: Convert remaining system module routes to use attributes
• #3593667: Convert user.module routes to attributes
• #3593666: Convert Views routes to attributes
• #3617973: Convert remaining test routes to attributes

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet