Add tests to cache_template_loading when an engine loaded Action View
before the application

This test is a regression test to
b068e20b35797aa6deaa377a48c990759734f515 that changed the load order of
Action View initializers.
Assert the singleton instead of to truthy/falsy

This will avoid false positives where caching? is nil and should be
false
Remove the explicit order set for the initializer

This will fix the regression added on
b068e20b35797aa6deaa377a48c990759734f515.

See tests added at ff08d31 to a better understanding about the problem
Merge branch 'av-loading-order'