Add patch package to apply diff changes to schemas

[jdolle]

Description

This change began as one to only the adds fields that are necessary for recreating the patched schema using the input schema and changes array, but it has expanded to also add the patch functionality. I found this was necessary in order to verify that the changes provided sufficient data.

This PR modifies the several change types, and modifies the onAdded handlers to also execute equivalent logic to onMutual. It also adds a new rule that can be added to filter out these additional changes, thus keeping changelogs to a minimum. Paths also needed changed to consistently and uniquely map to the node being changed. Previously, some changes referenced a parent's coordinate. Lastly, directives support was dramatically improved and the directive path was modified to include @ to distinguish it from any other node potentially with the same name.

The expansion of "onAdded" has a few down sides and an important up side.

Cons

1. Increased noise when listing changes
2. Increased complexity because it blurs the line between changes and additions. Although arguably some of the changes did this already.
3. It requires adjusting some of the criticality of these changes when they are created from within the onAdded call. Because e.g. adding an interface to newly create object is completely safe, but adding an interface to an existing object is considered dangerous.

Pro

1. Each change is represented as an event, so it the actual logic and mapping is simple. It's just the number of possible changes that makes this complex.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

See unit tests.

Checklist:

• I have followed the
  CONTRIBUTING doc and the
  style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[dotansimha]

LGTM. I added a few minor comments, mainly around release pipeline.
We can proceed once @n1ru4l confirms it's good to go.
Thanks!