Cleanup: use printn/print instead of printfn/printf for interpolated strings

[charlesroddie]

Prior to print(n), we could not print interpolated strings directly using FSharp syntax, and had to go through a formatted string path (printf(n) $"..."). This PR starts to use print(n) for these cases.

The advantages are simpler types and reduced cognitive complexity, improved performance, and being able to benefit from the new changes in interpolated strings (fsharp/fslang-suggestions#1468 (comment)).

Moreover, the less printf there is in public code, including the FSharp repo, the less AIs will use it.

Details

This PR replaces printfn $"..." with printn $"..." and printf $"..." with print $"..." (FS-1125) where the referenced FSharp.Core has them, and removes the one redundant sprintf before an interpolated string.

Changed

• FSharp.Core XML doc examples (set, async, eventmodule, observable, array2, array3)
• Commented-out code in FSharp.Core, the compiler, FSharp.Editor and coroutines.fsx
• FSharp.Core.UnitTests (always references the FSharp.Core project)
• eng/tests/TestSplit.fsx (runs on the SDK's FSharp.Core)
• TheBigFileOfDebugStepping.fsx (manual walkthrough compiled with the repo's fsc)
• RemoveUnnecessaryParenthesesTests (syntax-only inputs; continuation lines align with the function name, so layout is unchanged)
• TransparentCompiler.fs: sprintf $"F%03d{i}" → $"F%03d{i}"

Not changed

• Code in projects in FSharp.Compiler.Service.slnx (including tests/scripts/scriptlib.fsx): with FSHARPCORE_USE_PACKAGE=true they build against the shipped FSharp.Core 10.0.101, which lacks print/printn.
• Test source compiled at test time: breaks when tests run against the package FSharp.Core, and some snippets have IL baselines. Tests about printf itself (TypedInterpolatedStringsTests, StringFormatAndInterpolation) stay regardless.
• Other sprintf $ uses: they test sprintf $ itself (printf-interpolated/test.fsx, StringInterpolation.fs, EditorTests.fs) or describe that code path (printf.fs).
• Benchmarks, .github diagnostics server, docs/fcs: FSharp.Core 10 or own tooling.
• printf.fsi: those examples document printf/printfn.

The remainder can follow once the shipped FSharp.Core pin moves to 11.

🤖 Generated with Claude Code

[github-actions]

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[github-actions]

🔍 Tooling Safety Check — Affects-Build-Infra, Affects-Test-Tooling
Affects-Build-Infra: TestSplit script executes within build and CI workflows.
Affects-Test-Tooling: TestSplit controls generated test execution commands.

Generated by PR Tooling Safety Check · gpt56 1.1M · ◷

[Happypig375]

Should also implement a warning against using printf with $.

[T-Gro]

🤖 🕵️ LGTM