refactor(core): Update zone and zoneless error to be a warning instead - #63457

This updates the error thrown when both `provideZoneChangeDetection` and
`provideZonelessChangeDetection` are both used in the application
providers to be a warning instead. The reasons for this are twofold:

1. The migration we need for using zoneless by default isn't perfect and
   may add `provideZoneChangeDetection` when the zoneless provider
   exists. This change will prevent that from causing an error
2. There might be valid situations where a "default" is used in a common
   provider but that can be overridden by individal applications. In
   tests, we do allow this type of thing, where `initTestEnvironment`
   may have a default but individual tests might want to use a different
   one. The same logic might apply to applications in some environments.