`ldp.resource.patch`: detect if triples are really added or removed

## Problem

If `ldp.resource.patch` is called but the some of the `triplesToAdd` already exist, it will have no impact on the dataset. But in this case, we should not send these triples (as `triplesAdded`) in the `ldp.resource.patched` event.

Similarly, if some of `triplesToRemove` don't exist, they should not be sent (as `triplesRemoved`) in the `ldp.resource.patched` event.

## Proposed solution

First filter triples that are already added or removed.

If no triples are added or removed:
- Don't throw an error (this is OK)
- Don't do the SPARQL update
- Do not send the `ldp.resource.patched` event

Start at the ldp.resource.patch entry point and trace how triplesToAdd and triplesToRemove are checked before the update and patched event. Verify against the current dataset that existing additions and missing removals are omitted, and that empty effective sets cause no update, error, or event.

Written by the indexing model from the issue text.