Fix tests in `Extensions/ExtensionCommandTests.cs`

[andyleejordan]

This entire test file is commented out with a note:

PowerShellEditorServices/test/PowerShellEditorServices.Test/Extensions/ExtensionCommandTests.cs

Lines 21 to 23 in 945d616

	// TODO:
	// These tests require being able to instantiate a language server and use the service provider.
	// Re-enable them when we have mocked out more infrastructure for testing.