This PR significantly enhances the C# value equality documentation to address critical gaps in guidance around polymorphic equality and records containing reference-equality members.

Issues Addressed

1. Polymorphic Equality Problem
The existing documentation showed an implementation that fails in polymorphic scenarios:

TwoDPoint p1 = new ThreeDPoint(1, 2, 3);
TwoDPoint p2 = new ThreeDPoint(1, 2, 4);
Console.WriteLine(p1.Equals(p2)); // Returns True - incorrect!

This happens because the compiler selects the IEquatable<TwoDPoint> implementation based on compile-time type, ignoring the Z coordinate difference.

2. Records with Reference-Equality Members
While records are recommended for value equality, they don't work correctly when containing collections or other reference types:

public record PersonWithHobbies(string Name, List<string> Hobbies);

var person1 = new PersonWithHobbies("Alice", new List<string> { "Reading", "Swimming" });
var person2 = new PersonWithHobbies("Alice", new List<string> { "Reading", "Swimming" });

Console.WriteLine(person1.Equals(person2)); // False - different List instances!

Solutions Implemented

Explicit Interface Implementation for Safe Polymorphic Equality
Added a comprehensive section demonstrating how to use explicit interface implementation for IEquatable<T> to force all equality comparisons through the virtual Equals(object?) method:

bool IEquatable<TwoDPoint>.Equals(TwoDPoint? p) => Equals((object?)p);

protected virtual bool Equals(TwoDPoint? p)
{
    // Runtime type checking ensures correct behavior
    if (this.GetType() != p.GetType()) return false;
    // ... rest of implementation
}

Records with Collections Guidance
Added detailed documentation explaining why records fail with collections and providing solutions including custom IEquatable<T> implementations for content-based comparison.

Changes Made

• Enhanced record documentation with prominent warnings about reference-equality members
• Added "Records with collections" section with working examples showing the problem and solutions
• Added "Polymorphic equality" section with safe implementation using explicit interface implementation
• Created comprehensive code examples that compile and demonstrate both problems and solutions
• Updated cross-references to related documentation on explicit interface implementation
• Improved flow and structure of the overall documentation

All code examples have been tested and compile successfully, demonstrating the correct behavior for both problematic scenarios and their solutions.

Fixes #45164.

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