[dotnet] Add nullability annotations to print types

[RenderMichael]

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Description

This adds nullability annotations to the PDF-print stack, as well as documenting potential exceptions alongside some code modernization.

Motivation and Context

Contributes to #14640

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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PR Type

Enhancement, Bug fix, Tests

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Description

• Enabled nullability annotations across multiple classes to improve code safety and clarity.
• Added detailed exception documentation to constructors and methods to specify potential errors.
• Refactored properties to use auto-properties for cleaner code.
• Added validation checks and exception handling for invalid input values in PrintOptions.
• Enhanced test coverage by adding tests for invalid page numbers, ranges, and negative values.

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Changes walkthrough 📝

	Relevant files
Enhancement	EncodedFile.cs Add nullability and refactor EncodedFile class                      dotnet/src/webdriver/EncodedFile.cs Enabled nullability annotations. Added exception documentation for constructor. Refactored properties to use auto-properties. Simplified ToString method. +14/-17  ISupportsPrint.cs Add nullability and exception documentation to ISupportsPrint dotnet/src/webdriver/ISupportsPrint.cs Enabled nullability annotations. Added exception documentation for Print method. +7/-2      PrintDocument.cs Enhance PrintDocument with nullability and exceptions        dotnet/src/webdriver/PrintDocument.cs Enabled nullability annotations. Added exception documentation for constructor and SaveAsFile method. +17/-0    PrintOptions.cs Improve PrintOptions with nullability and validation          dotnet/src/webdriver/PrintOptions.cs Enabled nullability annotations. Added exception handling for invalid values. Refactored properties and methods for clarity. +89/-79  Screenshot.cs Add nullability and exceptions to Screenshot class              dotnet/src/webdriver/Screenshot.cs Enabled nullability annotations. Added exception documentation for constructor. +9/-0
Bug fix	WebDriver.cs Add null check in WebDriver Print method                                  dotnet/src/webdriver/WebDriver.cs Added null check for printOptions in Print method. +6/-0
Tests	PrintTest.cs Add validation tests for PrintOptions                                        dotnet/test/common/PrintTest.cs Added tests for invalid page numbers and ranges. Added tests for negative page sizes and margins. +34/-0

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[qodo-code-review]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 3 🔵🔵🔵⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Validation Gap The AddPageRangeToPrint method validates the start page is >= 1 but allows end page to be int.MaxValue without validation. Consider adding an upper bound validation. Possible Bug The ToDictionary method returns null values in the dictionary which could cause issues for consumers. Consider filtering out null values or documenting this behavior. Error Handling The SaveAsFile method checks for null/empty filename but doesn't validate file extension or path validity before attempting to write.

[qodo-code-review]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Score
General	Specify non-nullable dictionary value type to better reflect actual usage The ToDictionary() method should specify a non-nullable return type since all dictionary values are non-null. Change the return type from Dictionary<string, object?> to Dictionary<string, object>. dotnet/src/webdriver/PrintOptions.cs [187] -internal Dictionary<string, object?> ToDictionary() +internal Dictionary<string, object> ToDictionary() Apply this suggestion Suggestion importance[1-10]: 5 Why: The suggestion improves type safety by making the dictionary value type non-nullable since the code never adds null values. This enhances code clarity and prevents potential null-related issues.	5
	Initialize collection fields in constructor to ensure proper object initialization The pageRanges field should be initialized in the constructor rather than at declaration to ensure proper initialization in all cases. dotnet/src/webdriver/PrintOptions.cs [57] -private readonly HashSet<object> pageRanges = new HashSet<object>(); +private readonly HashSet<object> pageRanges; +public PrintOptions() +{ + pageRanges = new HashSet<object>(); +} + Apply this suggestion Suggestion importance[1-10]: 3 Why: While the suggestion follows a good practice of initializing collections in constructors, the current field initialization is already safe and works correctly. The change would be mostly stylistic with minimal impact.	3

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[nvborisenko]

Thanks @RenderMichael, safe to merge (if CI is green), after release process of 4.27 is finished.

[nvborisenko]

Please fix one comment.

[RenderMichael]

Thanks!

I saw the recent 4.27 release; it was nice to see the .NET release notes section longer than previous releases.

[nvborisenko]

The changes are not related to failed CI tests (ShadowRoot). Merging it.