Apply finalizer-safe dispose pattern to all IAutoSizableCALayer implementations

[Copilot]

PR #33818 fixed finalizer crashes in MauiCALayer and StaticCAShapeLayer by guarding native calls behind if (disposing). Review comment correctly identified that StaticCALayer and StaticCAGradientLayer have the same issue.

Changes

All four IAutoSizableCALayer implementations now guard Detach() to prevent calling into potentially deallocated native CALayer objects during finalization:

protected override void Dispose(bool disposing)
{
    if (disposing)  // Only touch native objects during explicit disposal
    {
        _autosizeToSuperLayerBehavior.Detach();
    }
    base.Dispose(disposing);
}

Modified:

• MauiCALayer.cs
• StaticCAShapeLayer.cs
• StaticCALayer.cs ← new
• StaticCAGradientLayer.cs ← new

Existing test MauiCALayerAutosizeToSuperLayerBehavior_DoesNotLeak validates all four classes.

Original prompt

Please review the following comment #33818 (review) from that PR and please create a new PR that addresses the comment

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