[ZEN-3764] Example Data: Generate example dummy data into OpenAPI Model from single schema (DO NOT MERGE)

[nbhusare]

This PR add's support for providing example data in the KZOE editor, in the form of a proposal provider. It introduces a new extension point named com.reprezen.swagedit.core.exampleprovider. Plug-ins having a dependency on com.reprezen.swagedit.core can provide an extension to the aforementioned extension point. The extension receives a resolved schema instance as input, which can be used with libraries like Adobe Ride (model-util), JSON Schema Faker... to generate dummy data.

It also enhances the internal utility API by adding two new classes - ModelUtils and ExtensionUtils. ModelUtils has API for traversing the JSON Node model (AST) and retrieving nodes with a given name. The ExtensionUtils adds support for reading extension points.

JsonExampleProposalProvider is the base class of the newly introduced example providers for Swagger and OpenAPI 3.0. The implementations OpenApi3ExampleProposalProvider and SwaggerExampleProposalProvider provide intelligence of identifying the content assist location and retrieving the ExampleProvider implementation.