Fix #18086: suppress NuGet restore stdout under FSI --quiet

[T-Gro]

Summary

When --quiet ( cConfigB.noFeedback) is active, route the captured stdout of the NuGet restore subprocess to stderr instead of stdout so that warnings like NU1608 and MSBuild Determining projects to restore... chatter no longer pollute FSI stdout.

Default (non-quiet) behavior is unchanged.
esult.StdError continues to go to stderr unconditionally.

Changes

• src/Compiler/Interactive/fsi.fs – When
  oFeedback is set, redirect restore stdout to stderr instead of stdout.
• ** ests/.../FsiCliTests.fs** – Add a test verifying that --quiet suppresses NuGet restore stdout.
• Release notes – Added entry under Fixed for 11.0.100.

Fixes #18086

[github-actions]

❗ Release notes required

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Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md	No current pull request URL (#19808) found, please consider adding it

[T-Gro]

Review: LGTM - Clean, well-targeted fix.

The change correctly routes NuGet restore stdout to Console.Error under --quiet mode while preserving it for users who redirect stderr. This is a reasonable design choice — slightly different from other noFeedback paths that use nullOut (full discard), but defensible since this is external process output that users may still want access to.

Tests are well-structured and cover the key scenarios (quiet suppresses NuGet chatter, default mode still works, user output still reaches stdout).

Minor suggestion: Consider adding Assert.Equal(0, result.ExitCode) in the FSI quiet mode suppresses NuGet restore output from stdout test for extra robustness — if NuGet resolution fails due to network issues, the test would fail with a clearer signal than the marker assertion.