[pp-1] Clean up plugin getter methods for views plugins

Problem/Motivation

Postponed on #941970: Only set router rebuild needed when something related to routing actually changes

@graber pointed out it would be good to clean up the getter methods:

Plugin getter methods cleanup (naming and logic), use of a single public method that gets all plugins for both the DisplayPluginBase ::calculateDependencies() and the new View::postSave() logic.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet