EnC Scenario: deleting a file doesn't display rude edit

[isadorasophia]

Version Used:

Steps to Reproduce:

1. Create a Console App (.NET Core) with the following code on Program.cs:

class Program 
{
    int a = 20;
    return;
}

2. Start debugging (F10);
3. Delete Program.cs externally;

Expected Behavior:

• EnC reports an error that the file has been deleted.

Actual Behavior:

• You can continue debugging without source code.

Remarks
*If you create a .NET Framework Console App instead, Roslyn emits a rude edit as long as you also close the code in the editor window. However, no message shows up on "Error List" Window.
*We might want to deal with file renames as well?

[tmat]

Moving to backlog. It is low priority as it requires the user to delete file outside of VS (VS project system does not allow file deletion during debugging).