Remove AntialiasThreshold from GraphicsOptions

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

Drops the AntialiasThreshold field/property from GraphicsOptions and updates related XML docs to reflect the simplified antialiasing behavior. Clone logic and test coverage were adjusted accordingly, including removal of threshold assertions and comparer checks.

[Copilot]

Pull request overview

This PR removes the AntialiasThreshold API surface from GraphicsOptions and updates related cloning behavior and tests to match the simplified antialiasing configuration model.

Changes:

• Removed AntialiasThreshold from GraphicsOptions and updated XML documentation accordingly.
• Updated deep-clone logic to no longer copy the removed property.
• Adjusted test utilities and unit tests by removing threshold-related assertions/comparisons.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/ImageSharp/GraphicsOptions.cs	Removes AntialiasThreshold and updates cloning + docs to reflect the simplified antialiasing configuration.
tests/ImageSharp.Tests/GraphicsOptionsTests.cs	Removes default/clone assertions that referenced the deleted threshold property.
tests/ImageSharp.Tests/TestUtilities/GraphicsOptionsComparer.cs	Removes threshold from the value equality comparison used by tests.

Suppressed comments (1)

tests/ImageSharp.Tests/TestUtilities/GraphicsOptionsComparer.cs:14

• GraphicsOptionsComparer implements value-based equality but GetHashCode currently delegates to obj.GetHashCode(), which is reference-based for GraphicsOptions and violates the IEqualityComparer<T> contract. This can produce incorrect behavior if the comparer is ever used with HashSet/Dictionary (even in tests).

        && x.Antialias == y.Antialias
        && x.BlendPercentage == y.BlendPercentage
        && x.ColorBlendingMode == y.ColorBlendingMode;

    public int GetHashCode(GraphicsOptions obj) => obj.GetHashCode();

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.