the reva share manager is inefficient

[butonic]

stats every shared resource

	// TODO: This is a hack for now.
	// Can we do that cleaner somehow?
	// The `ListStorageSpaces` method in sharesstorageprovider/sharesstorageprovider.go needs the etags.
	shareMetaData := make(map[string]share.Metadata, len(res.Shares))
	for _, rs := range res.Shares {
		// Stat .. here, only for etag and mtime? and then we throw the rest away?
		sRes, err := s.Stat(ctx, &provider.StatRequest{Ref: &provider.Reference{ResourceId: rs.Share.ResourceId}})
		if err != nil {
			logger.Error().
				Err(err).
				Interface("resourceID", rs.Share.ResourceId).
				Msg("ListRecievedShares: failed to stat the resource")
			continue
		}
		if sRes.Status.Code != rpc.Code_CODE_OK {
			logger.Error().
				Interface("resourceID", rs.Share.ResourceId).
				Msg("ListRecievedShares: failed to stat the resource")
			continue
		}
		shareMetaData[rs.Share.Id.OpaqueId] = share.Metadata{ETag: sRes.Info.Etag, Mtime: sRes.Info.Mtime}
	}

The sharesstorageproevider not only needs the etag and mtime. It may need a full stat response to build the virtual share jail #3719

The sharesstorageprovider should make the stat requests itself. PR in cs3org/reva#2885

And it can omit that for unmounted shares ... which brings us to the next issue...

cannot filter by un/accepted shares

When listing mountpoints unaccepted shares can be omitted. The CS3 API needs a filter to allow filtering.
tracked in #3843

[butonic]

also: cs3org/reva#2881

[micbar]

@butonic is this enough?

[micbar]

Done by #4431 and #4436 and #4539 and #4430