fix(federation): merge errors for shared root fields correctly

[ardatan]

Handle errors coming from subgraphs correctly when a root field is shared by different subgraphs

• If subgraph A returns an error for Query.foo, and subgraph B returns the data, ignore the error and keep it for null fields.
• If both subgraphs return errors, return them as AggregateError then return them to the gateway result.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7fe3587

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@graphql-tools/federation	Patch
federation-benchmark	Patch

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[github-actions]

✅ Benchmark Results

     ✓ no_errors
     ✓ expected_result

     checks.........................: 100.00% ✓ 324      ✗ 0  
     data_received..................: 38 MB   3.8 MB/s
     data_sent......................: 139 kB  14 kB/s
     http_req_blocked...............: avg=4.06µs   min=2.02µs   med=2.68µs   max=179.99µs p(90)=3.92µs   p(95)=4.22µs  
     http_req_connecting............: avg=716ns    min=0s       med=0s       max=116.09µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=57.53ms  min=48.97ms  med=54.02ms  max=156.29ms p(90)=63.16ms  p(95)=87.68ms 
       { expected_response:true }...: avg=57.53ms  min=48.97ms  med=54.02ms  max=156.29ms p(90)=63.16ms  p(95)=87.68ms 
     http_req_failed................: 0.00%   ✓ 0        ✗ 162
     http_req_receiving.............: avg=142.59µs min=106.85µs med=134.49µs max=382.91µs p(90)=160.12µs p(95)=173.66µs
     http_req_sending...............: avg=26.02µs  min=19.78µs  med=24.68µs  max=93.27µs  p(90)=30.67µs  p(95)=36.91µs 
     http_req_tls_handshaking.......: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=57.36ms  min=48.81ms  med=53.87ms  max=155.93ms p(90)=63.02ms  p(95)=87.52ms 
     http_reqs......................: 162     16.17489/s
     iteration_duration.............: avg=61.8ms   min=52.96ms  med=58.19ms  max=160.21ms p(90)=68.33ms  p(95)=91.57ms 
     iterations.....................: 162     16.17489/s
     vus............................: 1       min=1      max=1
     vus_max........................: 1       min=1      max=1

[github-actions]

🚀 Snapshot Release (alpha)

The latest changes of this PR are available as alpha on npm (based on the declared changesets):

Package	Version	Info
@graphql-tools/executor-http	1.1.5-alpha-20240718123353-7fe3587eed6cb8a9f672a63184b5acaede6538e5	npm ↗︎ unpkg ↗︎
@graphql-tools/federation	2.1.2-alpha-20240718123353-7fe3587eed6cb8a9f672a63184b5acaede6538e5	npm ↗︎ unpkg ↗︎

[github-actions]

💻 Website Preview

The latest changes are available as preview in: https://2697a53f.graphql-tools.pages.dev