Standard license headers across repo

[stephentoub]

We previously had a three-line license header on every file, except for files imported previously from mono, where we used a modified two-line license header on top of the one already there. The new guidance is to use a new two-line license header everywhere, such that we can have the same header regardless of whether the header originated in mono or not, and we can then enforce it via an editorconfig/analyzers/etc.

This PR automates the majority of the headers to be changed over.

This was done entirely with this (except for the addition to the .editorconfig file):

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;

class Program
{
    static void Main()
    {
        var utf8NoBom = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: false);

        foreach (string path in Directory.EnumerateFiles(@"d:\repos\runtime\src\", "*", SearchOption.AllDirectories))
        {
            string[] lines = File.ReadAllLines(path);

            List<string> result = null;
            if (lines.Length >= 3 &&
                lines[0].Trim() == "// Licensed to the .NET Foundation under one or more agreements." &&
                lines[1].Trim() == "// The .NET Foundation licenses this file to you under the MIT license." &&
                lines[2].Trim() == "// See the LICENSE file in the project root for more information.")
            {
                result = new List<string>(lines);
                result.RemoveAt(2);
            }
            else if (lines.Length >= 2 &&
                lines[0].Trim() == "// Licensed to the .NET Foundation under one or more agreements." &&
                lines[1].Trim() == "// See the LICENSE file in the project root for more information.")
            {
                result = new List<string>(lines);
                result[1] = "// The .NET Foundation licenses this file to you under the MIT license.";
            }

            if (result != null)
            {
                bool bad = false;
                for (int i = 0; i < lines.Length && !bad; i++)
                {
                    foreach (char c in lines[i])
                    {
                        if (c >= 0x80)
                        {
                            Console.WriteLine(path + " @ " + i);
                            bad = true;
                            break;
                        }
                    }
                }


                if (!bad)
                {
                    File.WriteAllLines(path, result, utf8NoBom);
                }
            }
        }
    }
}

I will follow up subsequently to convert the stragglers, e.g. files with non-ASCII characters, VB, etc. I can also use the above to redo this at any time if we'd prefer to close this for now for whatever reason, e.g. concerns about conflicts, there's a better way to do it, etc.

cc: @richlander, @jkotas, @danmosemsft, @jeffschwMSFT

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[stephentoub]

Heh, this is a first for me:

[stephentoub]

/azp help

[GrabYourPitchforks]

So that's why you wanted us to get to zero open PRs. ;)

[stephentoub]

/azp list

[GrabYourPitchforks]

I think there are so many files you broke the bot.
/azp run

[GrabYourPitchforks]

Kicked off the pipeline manually -> https://dev.azure.com/dnceng/public/_build/results?buildId=715585

[stephentoub]

fatal: reference is not a tree: db400d8b3af860b3228d3c78a3eac00d3124a908

[stephentoub]

I pushed my commit as a branch to dotnet/runtime and kicked it off manually with that:
https://dev.azure.com/dnceng/public/_build/results?buildId=715595
We'll see if it makes more progress...

[GrabYourPitchforks]

That'll probably work better. Both of the manual jobs I kicked off failed, probably because I didn't specify something correctly in the pipeline.