.NET: Update AIContextProviders to use Microsoft.Extensions.Compliance.Redaction (#4854)

* Update providers to use Microsoft.Extensions.Compliance.Redaction

* Fix formatting.

* Fix readme

dotnet/src/Shared/Redaction/README.md

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+# Redaction
+
+Log data redaction utilities built on `Microsoft.Extensions.Compliance.Redaction.Redactor`.
+
+Provides `ReplacingRedactor`, an internal `Redactor` implementation that replaces
+any input with a fixed replacement string (e.g. `"<redacted>"`).
+
+To use this in your project, add the following to your `.csproj` file:
+
+```xml
+<PropertyGroup>
+  <InjectSharedRedaction>true</InjectSharedRedaction>
+</PropertyGroup>
+```
+
+You will also need to add a package reference to `Microsoft.Extensions.Compliance.Abstractions`:
+
+```xml
+<ItemGroup>
+  <PackageReference Include="Microsoft.Extensions.Compliance.Abstractions" />
+</ItemGroup>
+```
+
+And finally, this also depends on the shared Throw class, so when using redaction, InjectSharedThrow should also be enabled:
+
+```xml
+<PropertyGroup>
+  <InjectSharedThrow>true</InjectSharedThrow>
+</PropertyGroup>
+```

dotnet/src/Shared/Redaction/ReplacingRedactor.cs

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+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using Microsoft.Extensions.Compliance.Redaction;
+using Microsoft.Shared.Diagnostics;
+
+namespace Microsoft.Agents.AI;
+
+/// <summary>
+/// A <see cref="Redactor"/> that replaces the entire input with a fixed replacement string.
+/// </summary>
+internal sealed class ReplacingRedactor : Redactor
+{
+    private readonly string _replacementText;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ReplacingRedactor"/> class.
+    /// </summary>
+    /// <param name="replacementText">The text to substitute for any input value.</param>
+    /// <exception cref="ArgumentNullException">Thrown when <paramref name="replacementText"/> is <see langword="null"/>.</exception>
+    public ReplacingRedactor(string replacementText)
+    {
+        this._replacementText = Throw.IfNull(replacementText);
+    }
+
+    /// <inheritdoc />
+    public override int GetRedactedLength(ReadOnlySpan<char> input) => this._replacementText.Length;
+
+    /// <inheritdoc />
+    public override int Redact(ReadOnlySpan<char> source, Span<char> destination)
+    {
+        this._replacementText.AsSpan().CopyTo(destination);
+        return this._replacementText.Length;
+    }
+}