Consume IFileWatcherService from CPS

[LittleLittleCloud]

What does this PR do

This PR consumes the IFileWatcherService from CPS in LaunchSettingsProvider class so we can avoid create another system file watcher in project cone

relevant issues

• [BUG] Unable to watch for changes in this large workspace folder microsoft/vscode-dotnettools#360
• [C# Dev Kit] Enable VS Code File watcher in C# Dev Kit
• [C# Dev Kit] LaunchSettingsProvider creates a high number of watchers in linux that are excluded via "files.watcherExclude"

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR introduces a new public interface IFileWatcherService and integrates it into LaunchSettingsProvider, enabling support for file watching via MEF. It updates both production and test code to stop using the legacy SimpleFileWatcher and instead use the injected IFileWatcherService.

• Updated tests to pass a mock IFileWatcherService and remove direct use of SimpleFileWatcher.
• Refactored LaunchSettingsProvider to implement IFileWatcherServiceClient, set up file watchers asynchronously, and handle file change notifications.
• Removed the legacy CleanupFileWatcher and related code to streamline file watcher management.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/Microsoft.VisualStudio.ProjectSystem.Managed.UnitTests/ProjectSystem/Debug/LaunchSettingsProviderTests.cs	Updated lambda formatting and constructor parameters to use the mock IFileWatcherService instead of creating a real file watcher.
src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/Debug/LaunchSettingsProvider.cs	Integrated IFileWatcherService and refactored file watcher setup/disposal with asynchronous registration and unregistration.

[drewnoakes]

Looks great. Thanks for banning the API too. I think that's a great improvement for future.

Left a few comments on minor things for you to take or leave at your discretion.

[davkean]

I think you want to think about these scenarios:

1. The project is renamed Nevermind, forgot that we don't rename the folder underneath.
2. The properties folder is renamed

[LittleLittleCloud]

I test the following scenarios

• renaming properties folder

It seems that in both main and this branch, renaming properties folder doesn't work.

• If the name of properties folder is Properties (default value), the folder can be renamed to other names like PropertiesA, but it can't be renaming back to Properties, with the following CPS warning
  
• If the name of properties folder is not the default value (Properties), then the folder can be renamed to other names that is not Properties and can be renaming back, but the launchSettingsProvider won't able to pick the updates from renamed launchSettings.json

The cause for the second issue is because we are not watching the folder change/renaming event, so LaunchSettingsProvider will not be notified if the folder of launchSettings.json get renamed. To address that issue, the LaunchSettingsProvider needs to be notified when the folder name of app designer properties get changed.

@drewnoakes @davkean how to listen for the changes of appdesigner properties folder name

[drewnoakes]

Given rename doesn't work on main, it's a nice-to-have here. Feels like an edge case. Great if we can make it work, but we don't have to hold this up on it. Maybe file it as an issue.

A scenario that I do think we should check is the outright deletion and recreation of the Properties folder, and of the launchSettings.json file. Do we do the right thing when the file/folder are deleted/created in all combinations?

[LittleLittleCloud]

A scenario that I do think we should check is the outright deletion and recreation of the Properties folder, and of the launchSettings.json file. Do we do the right thing when the file/folder are deleted/created in all combinations?

I created a tracking issue here: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2496401/ and assign myself to look at. Maybe the exact Properties name is held somewhere else given that folder with other names doesn't have that issue?

Given rename doesn't work on main, it's a nice-to-have here. Feels like an edge case. Great if we can make it work, but we don't have to hold this up on it. Maybe file it as an issue.

Seems that there's an issue to track that already: #2316
Maybe the launchSettingsProvider shouldn't cache the appdesignfolder.