Clarify .NET package and platform requirements for the data protection sample

[Copilot]

The data protection article's sample guidance was incomplete for modern .NET. Readers could resolve ProtectedData by adding the package, but the article didn't explain that requirement or that the ProtectedMemory portion remains .NET Framework-only.

• What changed

  • Added an upfront note that .NET on Windows requires the System.Security.Cryptography.ProtectedData NuGet package before you use ProtectedData or DataProtectionScope.
  • Expanded the compile guidance to distinguish modern .NET from .NET Framework.
  • Explicitly called out that ProtectedMemory and MemoryProtectionScope aren't supported on .NET, so the full sample doesn't compile there.

• Updated guidance

  • .NET Framework: use the article sample as written.
  • .NET: install System.Security.Cryptography.ProtectedData for the ProtectedData APIs, but don't expect the ProtectedMemory portion to compile.

• Example

  using System.Security.Cryptography;
  
  byte[] input = [1, 2, 3, 4];
  byte[] entropy = [5, 6, 7, 8];
  
  byte[] cipher = ProtectedData.Protect(input, entropy, DataProtectionScope.CurrentUser);
  byte[] plain = ProtectedData.Unprotect(cipher, entropy, DataProtectionScope.CurrentUser);

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Internal previews

📄 File	🔗 Preview link
docs/standard/security/how-to-use-data-protection.md	How to use data protection

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[adegeo]

@copilot ad a note in the example section that mentions the ProtectedMemory API isn't available on .NET (it's only available on .NET Framework) and that the methods EncryptInMemoryData and DecryptInMemoryData won't compile.

[Copilot]

@copilot ad a note in the example section that mentions the ProtectedMemory API isn't available on .NET (it's only available on .NET Framework) and that the methods EncryptInMemoryData and `Decryp...

Addressed in 57c0e05.

[BillWagner]

This LGTM. Let's