Add concrete examples to semantic versioning documentation for beginners

[Copilot]

This PR enhances the semantic versioning section in the C# versioning guide to better serve beginner developers by adding concrete, practical examples.

Problem

The current semantic versioning documentation was too abstract for beginners. A grade 8 student learning C# reported confusion about:

• What constitutes "incompatible API changes" (MAJOR version increments)
• What "backwards-compatible manner" means (MINOR vs PATCH increments)
• When to increment each version number type

Solution

Added a new subsection "Understanding version increments with examples" that provides:

MAJOR version examples (incompatible API changes):

• Removing public methods or properties
• Changing method signatures by adding required parameters
• Changing method behavior in breaking ways

MINOR version examples (backwards-compatible functionality):

• Adding new public methods or properties
• Adding optional parameters to existing methods
• Adding new method overloads

PATCH version examples (backwards-compatible bug fixes):

• Fixing bugs in existing method implementations
• Performance improvements that don't change the API

Each example includes clear "before and after" code samples showing the specific changes and version numbers, making it easy for beginners to understand the practical application of semantic versioning rules.

Key principle added

The key principle is: if existing code can use your new version without any changes, it's a MINOR or PATCH update. If existing code needs to be modified to work with your new version, it's a MAJOR update.

This simple rule helps developers quickly determine the appropriate version increment.

Fixes #23343.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/versioning.md	docs/csharp/versioning

[BillWagner]

This is a good start, but I have some comments.

[BillWagner]

This LGTM now.