Wrong SDK updated when Select Target Platform is used

[rbenegal]

Describe the bug
Support for Swift SDKs was added in #1191 however it seems like the wrong SDK may be updated.

To Reproduce
Steps to reproduce the behaviour:

1. Create a new Library project with >Swift: Create new project such as MyLibrary
2. Put some code in MyLibrary.swift such as:

import SwiftUI

public struct MyLibraryView: View {
  public init() {}  // Add an initializer if needed

    public var body: some View {
    VStack {
        Text("Hello")
    }
  }
}

4. Use Select Target Platform to switch to iOS
5. Reload Extensions using the prompt popup
6. Try to use code completion by changing Text("Hello") to something like

Text("Hello").frame(width: 100, height: 100, alignment: .center)

Code will not work, as it seems like the wrong SDK is being updated:

Also, it would be good to reduce to just one SDK setting to avoid confusion in the future.

.Expected behavior
Code completion should work correctly.

Environment

• OS: macOS 15.1
• Swift version (output of swift --version)
• swift-driver version: 1.116.1 Apple Swift version 6.1 (swiftlang-6.1.0.101.37 clang-1700.0.4.30)
  Target: arm64-apple-macosx15.0
• Visual Studio Code version: 1.96.4
• vscode-swift version: 2.0.0

[rbenegal]

In order to get things to work on iOS, I had to set swift.swiftSDK to arm64-apple-ios and click Reload the extensions on the prompt that pops up:

As well, once the settings are modified manually it seems like doing a Select Target Platform may no longer work to switch things back to another platform.

Once the settings are set correctly code completion and availability warnings should show up.

[matthewbastien]

Verified with a1a6b0f