Fix Type.IsVisible and Type.ContainsGenericParameters for function pointers

[Copilot]

• Understand the issue: Type.IsVisible and Type.ContainsGenericParameters don't handle function pointers correctly
• Modify ContainsGenericParameters in Type.Helpers.cs to check function pointer return and parameter types
• Modify IsVisible in Type.Helpers.cs to check function pointer return and parameter types
• Add tests for function pointer visibility with private types
• Add tests for function pointer ContainsGenericParameters with generic types
• Build and test the changes
• Run code review and address feedback
• Run CodeQL checker

Original prompt

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This section details on the original issue you should resolve

<issue_title>Abstract implementations of Type.IsVisible and Type.ContainsGenericParameters do not handle function pointers</issue_title>
<issue_description>### Description

Abstract implementations of Type.IsVisible and Type.ContainsGenericParameters do not handle function pointers

Reproduction Steps

unsafe
{
    Console.WriteLine(typeof(delegate* <string>).IsVisible);
    Console.WriteLine(typeof(delegate* <PrivateType>).IsVisible);
}


class PrivateType { }

Expected behavior

true false with dotnet run (correct).

Actual behavior

true true with PublishAot=true

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response</issue_description>

<agent_instructions>Handle function pointers in these two methods in Type.Helpers.cs. Make sure to add tests</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Abstract implementations of Type.IsVisible and Type.ContainsGenericParameters do not handle function pointers #122223

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[jkotas]

/azp run runtime-nativeaot-outerloop

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[Copilot]

Pull request overview

This PR fixes bugs in the abstract implementations of Type.IsVisible and Type.ContainsGenericParameters that caused incorrect results for function pointer types in NativeAOT.

Key Changes:

• Added function pointer handling to ContainsGenericParameters to check return and parameter types
• Added function pointer handling to IsVisible to validate visibility of return and parameter types
• Added comprehensive test coverage for function pointer visibility scenarios

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Private.CoreLib/src/System/Type.Helpers.cs	Adds function pointer checks to ContainsGenericParameters and IsVisible properties to recursively validate return and parameter types
src/libraries/Common/tests/System/FunctionPointerTests.cs	Adds FunctionPointerVisibility test with scenarios for public/private return types and parameters, plus supporting test fields in FunctionPointerHolder