Is your feature request related to a problem? Please describe.
A few abstract and test components are not marked as standalone, while the majority of them is.
Describe the solution you'd like
To enforce best practices and improve consistency in the code base, we might want to use the @angular-eslint/prefer-standalone linting rule.
Describe alternatives or workarounds you've considered
I think this is the best way to address these inconsistencies, since it is easily implemented and it is naturally executed via linting.