CPP-1103 Change x-teaser's props to match content-pipeline's Content

[ivomurrell]

The shape of x-teaser's props were historically designed to match the shape of data that was stored in ElasticSearch. Now the data's shape is declared in cp-content-pipeline-schema as a GraphQL schema, and we should update the x-teaser properties to match. This will allow us to remove a hack that was previously in place in cp-content-pipeline-schema to support both the new Content type (which will subsequently be updated to provide all the metadata x-teaser needs) and the legacy Teaser type.

This is a breaking change for the component, which we can roll into one major release (v12), along with the changes to x-gift-article. We'll add a wiki page detailing how to migrate both of the components.