Expose ExitCode on ProcessException

[Baune8D]

• Expose the exit code on ProcessException.

It would be immensly useful to be able to get the actual exit code instead of parsing the error message.

I confirm that the pull-request:

• Follows the contribution guidelines
• Is based on my own work
• Is in compliance with my employer

[ron-myers]

Good work @Baune8D - I have wanted this a few times in the past.

[matkoch]

Next version is going to have this

DotNetRestore(_ => _
    .SetProjectFile(Solution)
    .DisableProcessAssertZeroExitCode());

DotNetRestore(_ => _
    .SetProjectFile(Solution)
    .SetProcessCustomExitHandler((_, p) =>
        p.ExitCode switch
        {
            0 => null,
            _ => throw new Exception()
        }));

DotNetRestore(_ => _
    .SetProjectFile(Solution + "aaaa")
    .SetProcessCustomExitHandler(p =>
    {
        switch (p.ExitCode)
        {
            case 1:
                break;
        }
    }));