Starred completions in the Language Server were implemented as a special IntelliCode extension integration path. Since that extension path is deprecated, this PR removes the StarredCompletions-specific code and simplifies startup/configuration and extension loading.

• Removed StarredCompletions feature implementation

  • Deleted Services/StarredCompletions/StarredCompletionProvider.cs
  • Deleted Services/StarredCompletions/StarredCompletionsAssemblyHelper.cs

• Removed server startup/configuration plumbing

  • Dropped --starredCompletionComponentPath from Program.cs
  • Removed StarredCompletionAssemblyHelper.InitializeInstance(...) call
  • Removed StarredCompletionsPath from ServerConfiguration (ServerConfigurationFactory.cs)
  • Updated test configuration construction to stop passing StarredCompletionsPath

• Simplified extension assembly loading

  • Removed the special-case IntelliCode load-context hack in ExtensionAssemblyManager.Create(...)
  • Extension loading now only processes explicit extension assembly paths

Example of the config simplification:

internal sealed record class ServerConfiguration(
    bool LaunchDebugger,
    LogConfiguration LogConfiguration,
    string? TelemetryLevel,
    string? SessionId,
    IEnumerable<string> ExtensionAssemblyPaths,
    string? DevKitDependencyPath,
    string? RazorDesignTimePath,
    string? CSharpDesignTimePath,
    string? ServerPipeName,
    bool UseStdIo,
    string? ExtensionLogDirectory,
    bool AutoLoadProjects,
    SourceGeneratorExecutionPreference SourceGeneratorExecutionPreference,
    int? ClientProcessId);

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