[2877] Add support for breadcrumbs in Portals

[pcdavid]

No description provided.

[pcdavid]

Note that this version completely crashes the backend.

For some reason I don't yet completely understand, the editing context event processor stays blocked indefinitly on future.get() after submitting the () -> this.doHandle(payloadSink, input).
Well, not indefinitely in this version as I added a 5s timeout (which seems like a good idea anyway, though the actual value of delay is debatable and should probably be configurable).

Anyway, I don't really see how the new GraphQL field, data fetcher and handler I added are different from what's already done for RepresentationMetadataDescriptionDataFetcher.

In summary, the changes are:

// portal.graphqls
extend type RepresentationMetadata {
  breadcrumbs: [WorkbenchSelectionEntry!]!
}

The corresponding data fetcher is RepresentationMetadataBreadcrumbsDataFetcher and follows the same patterns as RepresentationMetadataDescriptionDataFetcher:

• read the data from the GraphQL environment
• create a custom input record, here a RepresentationBreadcumbsInput instead of a GetRepresentationDescriptionInput
• the actual handling is done in RepresentationBreadcrumbEventHandler which emit a RepresentationBreadcrumbsSuccessPayload (instead of a GetRepresentationDescriptionPayload) and ChangeKind.NOTHING change description.

The only difference I see is that on the front:

• I fetch (possibly) multiple "instances" of this field, one for each representation embedded inside a portal:

views {
  id
  representationMetadata {
    id
    kind
    label
    breadcrumbs {
      id
      kind
      label
    }
  }
}

• this is done in the context of a subscription and not a plain query.

@sbegaudeau do you see what I'm doing wrong?

[pcdavid]

PS: ignore the fact that in this version the handler hard-codes the computation of the breadcrumbs using EMF-specific code. This was just for the initial PoC.