[2.0][DX] Suggested dependencies and version constraint

Some suggested package, such as `doctrine-fixtures-bundle` requires a specific version to work (for fixtures it's 3.0), but because they are only `suggested` dependencies, no check are done on the version.

So someone that have the `doctrine-fixtures-bundle` in 2.0 will see a message `doctrine/doctrine-fixtures-bundle must be installed to use this method.` (per #437) but nothing related to the version.

Not sure how it can be handled in a clean way.

Review the suggested-dependency handling described for doctrine-fixtures-bundle and compare it with the missing-dependency message referenced from #437. Determine how a version constraint could be checked or reported; done means users with an incompatible version receive a useful version-specific message rather than only an installation warning.

Written by the indexing model from the issue text.