Support composite foreign keys

[phanbaominh]

Summary

• Add support for composite foreign key (import, export, parsing).
• An example of the new composite foreign keys syntax for dbml:
  products.(id, name) < order_items.(product_id, product_name).
• Still support the old syntax: products.id < order_items.product_id.

Issue

Lasting Changes (Technical)

• Change all parser.pegjs files and exporters to support composite foreign key (in ref section).
• Endpoint normalized form's fieldId is replaced by fieldIds (array).
• Endpoint's fieldName, field is replace by fieldNames, fields (array).
• Change Endpoint#equals.
• Add error handling for when two endpoints have different number of fields in Ref object.
• Add buildFieldName to export/utils for building a field names string when exporting.
• Change (mostly in test files that have foreign keys definition) and add (mostly in referential_actions test files) new test cases .

Checklist

Please check directly on the box once each of these are done

• Documentation (if necessary)
• Tests (integration test/unit test)
• Integration Tests Passed
• Code Review

[phuongduyphan]

Please fix eslint errors first @wingombia .

[phanbaominh]

As I see at all the places in this PR, this is always an array of names.
Suggest changing fieldName to fieldNames instead.

Why we have to divide into 2 cases in order to compare fields here? Can compareFields compare fields with length 1?

Why we need to set this.field = field here?

oops, I forgot to push the latest commits where I fixed these.

Edit: I have pushed the lastest commits that fix the problems stated in your comments.