Reinstate supplemental remarks (various)

[gewarren]

Contributes to #12613.

Also removes .NET Framework remarks.

[Copilot]

Pull request overview

This PR reintegrates “supplemental API remarks” content back into this repo by replacing the external “Supplemental API remarks” links with inlined markdown remarks across several API reference XML files. It also adds new snippet projects/files to support the expanded remarks content (notably for System.Numerics and System.Collections.Generic).

Changes:

• Replaced “Supplemental API remarks” links with inlined <remarks><format type="text/markdown">…</format></remarks> content across multiple XML API docs.
• Added new C#, Visual Basic, and F# snippet projects and sources referenced from the restored remarks.
• Updated/expanded several API pages with longer conceptual guidance (security notes, algorithm explanations, usage patterns).

Reviewed changes

Copilot reviewed 45 out of 45 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
xml/System.Security/SecureString.xml	Restores detailed remarks (including guidance and security limitations).
xml/System.Security.Cryptography/RSAParameters.xml	Restores detailed RSAParameters conceptual remarks and field summary.
xml/System.Security.Cryptography/RSACryptoServiceProvider.xml	Restores remarks about CSP key sizes and CAPI interop behavior.
xml/System.Security.Cryptography.Xml/SignedXml.xml	Restores extensive XMLDSIG/SignedXml usage + security considerations.
xml/System.Numerics/Complex.xml	Restores extensive Complex overview remarks and adds snippet references.
xml/System.Numerics/BigInteger.xml	Restores extensive BigInteger overview remarks and adds snippet references.
xml/System.Net/HttpListener.xml	Restores HttpListener overview remarks including security guidance and HTTP.sys notes.
xml/System.Net/FtpWebRequest.xml	Updates remarks for FtpWebRequest.Proxy property.
xml/System.Net.Sockets/Socket.xml	Restores Socket overview remarks and sync/async usage guidance.
xml/System.Net.Http/HttpClientHandler.xml	Restores remarks about HttpClientHandler and .NET Core implementation differences.
xml/System.Net.Http/HttpClient.xml	Restores long-form guidance on HttpClient instancing, pooling, transports, and options.
xml/System.Linq.Expressions/Expression.xml	Restores method-level remarks for Expression.Add overloads.
xml/System.Linq.Expressions/BinaryExpression.xml	Restores overview remarks summarizing binary expression factory methods.
xml/System.Collections.ObjectModel/ObservableCollection`1.xml	Restores overview remarks about data binding and XAML usage.
xml/System.Collections.ObjectModel/KeyedCollection`2.xml	Restores method remarks for ChangeItemKey.
xml/System.Collections.Generic/List`1.xml	Restores long-form List<T> overview + examples and snippet references.
xml/System.Collections.Generic/HashSet`1.xml	Restores long-form HashSet<T> overview remarks and set/LINQ comparisons.
xml/Microsoft.Win32/Registry.xml	Restores longer Registry overview remarks content.
snippets/visualbasic/System.Numerics/Complex/Overview/Project.vbproj	New VB snippet project for Complex overview.
snippets/visualbasic/System.Numerics/Complex/Overview/Program.vb	VB entrypoint for Complex overview snippet project.
snippets/visualbasic/System.Numerics/Complex/Overview/precision1.vb	VB snippet source for Complex precision examples.
snippets/visualbasic/System.Numerics/Complex/Overview/nan1.vb	VB snippet source for Complex NaN/Infinity examples.
snippets/visualbasic/System.Numerics/Complex/Overview/customfmt1.vb	VB snippet source for Complex custom formatting example.
snippets/visualbasic/System.Numerics/Complex/Overview/create1.vb	VB snippet source for Complex instantiation examples.
snippets/visualbasic/System.Numerics/BigInteger/Overview/Project.vbproj	New VB snippet project for BigInteger overview.
snippets/visualbasic/System.Numerics/BigInteger/Overview/Mutability_Examples.vb	VB snippet source for BigInteger mutability/perf examples.
snippets/visualbasic/System.Numerics/BigInteger/Overview/ByteAndHex_Examples2.vb	VB snippet source for BigInteger hex parsing example.
snippets/visualbasic/System.Numerics/BigInteger/Overview/ByteAndHex_Examples.vb	VB snippet source for BigInteger byte/hex roundtrip examples.
snippets/visualbasic/System.Numerics/BigInteger/Overview/BigInteger_Examples.vb	VB snippet source for BigInteger instantiation examples.
snippets/visualbasic/System.Collections.Generic/List/Overview/source.vb	New VB snippet source for List<T> overview examples.
snippets/visualbasic/System.Collections.Generic/List/Overview/Project.vbproj	New VB snippet project for List<T> overview.
snippets/visualbasic/System.Collections.Generic/List/Overview/module1.vb	New VB snippet source for List<T> business-object example.
snippets/fsharp/System.Collections.Generic/ListT/Overview/listclass.fs	New F# snippet for List<T> basics (ResizeArray).
snippets/fsharp/System.Collections.Generic/ListT/Overview/addremoveinsert.fs	New F# snippet for add/remove/insert example.
snippets/csharp/System.Numerics/Complex/Overview/Project.csproj	New C# snippet project for Complex overview.
snippets/csharp/System.Numerics/Complex/Overview/Program.cs	C# entrypoint for Complex overview snippet project.
snippets/csharp/System.Numerics/Complex/Overview/precision1.cs	C# snippet source for Complex precision examples.
snippets/csharp/System.Numerics/Complex/Overview/nan1.cs	C# snippet source for Complex NaN/Infinity examples.
snippets/csharp/System.Numerics/Complex/Overview/customfmt1.cs	C# snippet source for Complex custom formatting example.
snippets/csharp/System.Numerics/Complex/Overview/create1.cs	C# snippet source for Complex instantiation examples.
snippets/csharp/System.Numerics/BigInteger/Overview/Project.csproj	New C# snippet project for BigInteger overview.
snippets/csharp/System.Numerics/BigInteger/Overview/Mutability_Examples.cs	C# snippet source for BigInteger mutability/perf examples.
snippets/csharp/System.Numerics/BigInteger/Overview/ByteAndHex_Examples2.cs	C# snippet source for BigInteger hex parsing example.
snippets/csharp/System.Numerics/BigInteger/Overview/ByteAndHex_Examples.cs	C# snippet source for BigInteger byte/hex roundtrip examples.
snippets/csharp/System.Numerics/BigInteger/Overview/BigInteger_Examples.cs	C# snippet source for BigInteger instantiation examples.

Comments suppressed due to low confidence (1)

snippets/csharp/System.Numerics/Complex/Overview/precision1.cs:36

• These trailing comments are redundant (they restate code already shown) and contain a grammatical error ("where as") plus an incomplete IA64 sentence. Removing them avoids confusion.

// Complex minusOne = new Complex(-1,0);
// Complex.Sqrt(minusOne) returns Complex(6.12303176911189E-17, 1) where as it returns Complex on IA64.

[gewarren]

Snippets 5000 failures are for missing .fsproj files.