Document .NET 11 breaking change: Math.Round/MathF.Round with digits

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Math.Round(double, int[, MidpointRounding]) and MathF.Round(float, int[, MidpointRounding]) now round based on the exact value of the input rather than a value * 10^digits scaling approximation, changing results for some inputs; the digits cap (0-15 for double, 0-6 for float) has also been removed, so only negative values throw.

Changes

• New article docs/core/compatibility/core-libraries/11/math-round-digits.md — covers version introduced (.NET 11 Preview 7), previous vs. new behavior with examples, change category, rationale (link to Fix incorrect rounding in Math.Round and MathF.Round with digits runtime#130574), recommended action, and affected APIs.
• Index docs/core/compatibility/11.md — added row under Core .NET libraries.
• TOC docs/core/compatibility/toc.yml — added entry in the .NET 11 Core .NET libraries section.

Behavior contrast documented:

Math.Round(655.925, 2, MidpointRounding.AwayFromZero);            // was 655.93,             now 655.92
Math.Round(1111111111111111.5, 1, MidpointRounding.AwayFromZero); // was 1111111111111111.6, now 1111111111111111.5
Math.Round(1.5, 16, MidpointRounding.ToEven);                     // was ArgumentOutOfRangeException, now 1.5

The article also notes that the corrected behavior flows through double.Round, float.Round, Half.Round, and NFloat.Round, and that the decimal and single-argument overloads are unaffected.

• Fixes [Breaking change]: Math.Round/MathF.Round with digits return the correctly rounded result and accept any non-negative digit count #54762

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Internal previews

File	Preview link
docs/core/compatibility/11.md	docs/core/compatibility/11
docs/core/compatibility/core-libraries/11/math-round-digits.md	docs/core/compatibility/core-libraries/11/math-round-digits
docs/core/compatibility/toc.yml	docs/core/compatibility/toc

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