By reading from the definition from microsoft site below, it look like we grant view definition on server level, also add the user to the database without granting any permissions is equivalent as granting the user the view definition to the securables.

The VIEW DEFINITION permission lets a user see the metadata of the securable on which the permission is granted. However, VIEW DEFINITION permission does not confer access to the securable itself. For example, a user that is granted only VIEW DEFINITION permission on a table can see metadata related to the table in the sys.objects catalog view. However, without additional permissions such as SELECT or CONTROL, the user cannot read data from the table. For more information about viewing metadata,

You can grant VIEW DEFINITION permission to a user on a securable, for example a table. This lets the user see metadata of the table and any subcomponents that are related to the table, such as triggers, constraints, and indexes