Add ProcessExitStatus class to System.Diagnostics.Process

[Copilot]

Implementation Plan for ProcessExitStatus

• Add ProcessExitStatus to reference file (ref/System.Diagnostics.Process.cs)
• Add ProcessExitStatus implementation in src/System/Diagnostics/ProcessExitStatus.cs
• Add XML documentation based on the approved API shape
• Add basic unit tests for ProcessExitStatus
• Build and test the changes
• Address API review feedback - remove IEquatable and equality members
• Change from struct to sealed class per approved API shape
• Rename constructor parameter cancelled to canceled to match Canceled property
• Clarify Signal property remarks for publicly constructible type
• Improve Signal property docs to clarify it is a Unix-only concept

The API got approved in #123380 (comment)

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[adamsitnik]

@copilot address my feedback

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[Copilot]

@copilot address my feedback

Addressed in commit b291ae1. Removed IEquatable interface and all equality-related members to match the approved API shape.

[adamsitnik]

LGTM

[Copilot]

Pull request overview

Adds a new System.Diagnostics.ProcessExitStatus public type to represent process termination state (exit code, optional POSIX signal, and cancellation/timeout termination), along with unit tests and project file wiring to compile/ship the new API.

Changes:

• Added new public API ProcessExitStatus (ref + implementation) in System.Diagnostics.Process.
• Wired the new source file into the product csproj and added a new unit test file.
• Added unit tests validating constructor/property behavior for multiple parameter combinations.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/libraries/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests.csproj	Includes the new ProcessExitStatusTests.cs test file in compilation.
src/libraries/System.Diagnostics.Process/tests/ProcessExitStatusTests.cs	Adds unit tests for ProcessExitStatus constructor/property combinations.
src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessExitStatus.cs	Implements the new public ProcessExitStatus class with XML docs.
src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj	Adds ProcessExitStatus.cs to the product compilation list.
src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs	Adds the ProcessExitStatus public ref-surface declaration.

[stephentoub]

@copilot please invoke the code-review skill and post your analysis/results as a comment on this PR

[stephentoub]

@copilot please address the feedback

[Copilot]

@copilot please address the feedback

Addressed the remaining reviewer feedback — clarified the Signal property remarks from "This property is always null on Windows" to "When produced by Process APIs on Windows, this property is always null" since the type is publicly constructible (commit 9932cba). The cancelled → canceled rename was already done in 2f9f9f6.

[adamsitnik]

LGTM

[rzikm]

LGTM