Add comprehensive API documentation for GradientStop class

[Copilot]

Fixes dotnet/docs-maui#3162

• Understand issue [Bug] CollectionView Crash on Android using a custom header #3162 and documentation guidelines
• Review existing GradientStop.cs and GradientStop.xml files
• Examine usage patterns in test files and code examples
• Add XML documentation for GradientStop.Offset property
• Add XML documentation for GradientStop.Color property
• Add XML documentation for GradientStop class and constructors
• Format documentation and verify consistency
• Verify documentation follows CodeDocumentationGuidelines.md
• Remove T: and P: prefixes from all cref references
• Replace all "To be added" remarks with meaningful content

Original prompt

Please improve the API docs for GradientOffset as per this issue: dotnet/docs-maui#3162. Follow the documentation instructions from https://github.com/dotnet/maui/blob/main/docs/CodeDocumentationGuidelines.md

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[jfversluis]

@copilot don't add the "To be added." comments, remove them or add something meaningful. Additionally, don't use the T: and P: prefixes, use the strongly typed references

[Copilot]

@copilot don't add the "To be added." comments, remove them or add something meaningful. Additionally, don't use the T: and P: prefixes, use the strongly typed references

Updated in commit 10fa566:

• Removed all T: and P: prefixes from <see cref> references
• Replaced all "To be added" remarks with meaningful content or removed the remarks tag where appropriate

[Copilot]

Pull request overview

This PR adds comprehensive API documentation for the GradientStop class, addressing issue #3162. The documentation includes detailed summaries, remarks, parameter descriptions, and return value documentation for all public members following the Code Documentation Guidelines.

Changes:

• Added class-level documentation with summary and remarks explaining the purpose and usage of GradientStop
• Documented both constructors (default and parameterized) with summaries and remarks
• Added complete documentation for Color and Offset properties including summaries, value descriptions, and detailed remarks
• Documented BindableProperty identifiers for ColorProperty and OffsetProperty
• Added documentation for Equals and GetHashCode methods

[Copilot]

According to the Code Documentation Guidelines (line 14), bindable properties should have "This is a bindable property." at the END of the summary, not at the beginning. The summary should describe what the property does first, then end with "This is a bindable property."

For example, the summary should be structured as:
"Gets or sets the color of the gradient stop. This is a bindable property."

[Copilot]

According to the Code Documentation Guidelines (line 14), bindable properties should have "This is a bindable property." at the END of the summary, not at the beginning. The summary should describe what the property does first, then end with "This is a bindable property."

For example, the summary should be structured as:
"Gets or sets the position of the gradient stop within the gradient. This is a bindable property."