Add ParameterListStructureProvider for collapsing multi-line parameter lists

[Copilot]

Implements collapsing/expanding for multi-line parameter lists in VS Code and other Roslyn-powered editors, matching the existing behavior of ArgumentListStructureProvider.

Resolves #80946

Changes

• ParameterListStructureProvider.cs: New provider inheriting from AbstractSyntaxNodeStructureProvider<ParameterListSyntax> that enables collapsing when the opening ( and closing ) span 2+ lines
• CSharpBlockStructureProvider.cs: Registered ParameterListStructureProvider in the node provider map
• ParameterListSyntaxStructureTests.cs: Test coverage for methods, constructors, delegates, lambdas, anonymous methods, and local functions

Example

// Collapsible (line difference >= 2)
void ProcessData(
    string inputFile,
    string outputFile,
    bool validateData)
{
    // Can collapse to: void ProcessData(...)
}

// Not collapsible (line difference < 2)
void ProcessData(string inputFile,
    string outputFile)
{
    // No collapse indicator shown
}

Fixes https://github.com/dotnet/vscode-csharp/issues/8725

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Original prompt

Please resolve https://github.com/dotnet/vscode-csharp/issues/8725 by implementing a new ParameterListStructureProvider (likely inheriting from AbstractSyntaxNodeStructureProvider) and adding it to the list in CSharpBlockStructureProvider. Similar to the ArgumentListStructureProvider, only provide the structure if the parameter list is greater than or equal to 2 lines.

Please add tests for this as well. Look at ArgumentListSyntaxStructureTests for examples of existing tests.

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[dibarbet]

seems fine, but actually worsens the VSCode experience due to dotnet/vscode-csharp#7974 - causes the method folding ranges to disappear and you only get the parameter list range.

that needs to be fixed first before this can go in. leaving as draft for now.

[lonix1]

@dibarbet Thanks for taking a stab at this. I hope it can be completed when the blocker is removed.

One question: was the Copilot bot responsible for crafting the entire PR? That is absolutely mind boggling if true.

[dibarbet]

I hope it can be completed when the blocker is removed.

I am working on this, but it's definitely a bit more complicated. Our folding range providers aren't really designed to not have overlapping lines 😆

One question: was the Copilot bot responsible for crafting the entire PR? That is absolutely mind boggling if true.

It was indeed. It did a pretty good job on this one, I don't think I'll have to fix much here. You can see the specific prompt in the PR description under 'Original prompt' if you are curious.

[dibarbet]

Unfortunately in VSCode we can't make the experience perfect. The folding range for the method starts on the same line that the parameter folding range would end, and VSCode does not allow this overlap. So the parameter range gets shrunk by one, leading to the last parameter line being unfolded.

[JoeRobich]

Chatted offline about the >= 2 and it matches the behavior of the argument list provider.