Add support for patches.json

Problem/Motivation

The Composer Patches plugin reads from patches.json as well as from composer.json. Automatic Updates only copies composer.json.

Steps to reproduce

1. Move patches to patches.json.
2. Run composer install.
3. Run composer update to set Drupal to an outdated version.
4. Use Automatic Updates to update.
5. Patches are not applied.

Proposed resolution

Copy patches.json as well as composer.json.

Remaining tasks

1. Create branch to fix issue.
2. Review code.
3. Test.
4. Merge branch.

User interface changes

None.

API changes

Patches in patches.json are applied in automatic updates.

Data model changes

None.