Deprecate usage of @joincolumn on the inverse side of one-to-one associations

Following up on #10652:

 #### Current situation

The implementation of `\Doctrine\ORM\Mapping\ClassMetadataInfo::_validateAndCompleteOneToOneMapping` will consider a field with a one-to-one association to be the owning side also when it configures `@JoinColumn` settings.

 #### Suggested change

For a one to one association, a field should be the inverse side when it uses the `mappedBy` attribute, and be the owning side otherwise. The `JoinColumn` may be configured on the owning side only.

This PR adds a deprecation notice when `@JoinColumn` is used on the side of a one-to-one association where `mappedBy` occurs.

In 3.0, this will throw a `MappingException`.

Author: mpdude

UPGRADE.md

@@ -1,5 +1,12 @@
 # Upgrade to 2.15
 
+## Deprecated configuring `JoinColumn` on the inverse side of one-to-one associations
+
+For one-to-one associations, the side using the `mappedBy` attribute is the inverse side.
+The owning side is the entity with the table containing the foreign key. Using `JoinColumn`
+configuration on the _inverse_ side now triggers a deprecation notice and will be an error
+in 3.0.
+
 ## Deprecated overriding fields or associations not declared in mapped superclasses
 
 As stated in the documentation, fields and associations may only be overridden when being inherited

lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php

@@ -1864,6 +1864,14 @@ protected function _validateAndCompleteOneToOneMapping(array $mapping)
     {
         $mapping = $this->_validateAndCompleteAssociationMapping($mapping);
 
+        if (isset($mapping['joinColumns']) && $mapping['joinColumns'] && ! $mapping['isOwningSide']) {
+            Deprecation::trigger(
+                'doctrine/orm',
+                'https://github.com/doctrine/orm/pull/10654',
+                'JoinColumn configuration is not allowed on the inverse side of one-to-one associations, and will throw a MappingException in Doctrine ORM 3.0'
+            );
+        }
+
         if (isset($mapping['joinColumns']) && $mapping['joinColumns']) {
             $mapping['isOwningSide'] = true;
         }