Breakpoints can be inconsistent when UI sends files with different casing

[fabioz]

I just stumbled into a case where VSCode (1.66) sends a breakpoint such as:

{
    "arguments": {
        "breakpoints": [
            {
                "line": 477
            }
        ],
        "lines": [
            477
        ],
        "source": {
            "name": "File.py",
            "path": "c:\\python37\\lib\\File.py"
        },
        "sourceModified": false
    },
    "command": "setBreakpoints",
    "seq": 4,
    "type": "request"
}

But later on to remove the breakpoint it sends the file with a path with a different case:

{
    "arguments": {
        "breakpoints": [],
        "lines": [],
        "source": {
            "name": "File.py",
            "path": "c:\\python37\\Lib\\File.py"
        },
        "sourceModified": false
    },
    "command": "setBreakpoints",
    "seq": 4,
    "type": "request"
}

This makes it so that the debugger is not able to remove the breakpoint (because it considers that the original filename should be always the same one sent from the client, but apparently, this isn't always the case).