Fresh clone of repository results in many compilation errors

Start with a fresh clone and attempt the repository build, then inspect .editorconfig, Directory.Build.props, and nuget.config against the reported compilation and package-source failures. Check the README for build prerequisites and document or correct the repository configuration so a fresh checkout builds without local edits.

I want to investigate implementing S3 compatibility for this. As an initial stab I wanted to get this compiled and working in my local environment. I tested this about a year ago and it worked fine but since then it seems like there have been some regressions.

I wanted to outline the fixes I had to implement to get this compiling in hopes that someone more familiar with the repository can provide guidance on the correct fixes for the main branch.

https://github.com/microsoft/MSBuildCache/blob/c1faabb1d036689b2421342ccf1e747d96ab2cf5/.editorconfig#L377
Had to change that to dotnet_diagnostic.IDE0055.severity = none # Fix formatting because there were a significant amount of errors after opening the solution.

https://github.com/microsoft/MSBuildCache/blob/c1faabb1d036689b2421342ccf1e747d96ab2cf5/Directory.Build.props#L37
Had to update this to ignore security vulnerability errors <NoWarn>$(NoWarn);NU5104;NU1901;NU1902;NU1903</NoWarn>. There were a lot of NuGet packages being flagged for vulnerabilities and preventing compilation.

The NuGet.config (https://github.com/microsoft/MSBuildCache/blob/main/nuget.config) had to be updated because it was failing to retrieve packages.
I had to do this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="nuget" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
    <add key="msbuildcache" value="https://pkgs.dev.azure.com/msbuildcache/public/_packaging/msbuildcache/nuget/v3/index.json" />
  </packageSources>
  <packageSourceMapping>
    <clear />
    <packageSource key="nuget">
      <package pattern="*" />
    </packageSource>
    <packageSource key="msbuildcache">
      <package pattern="RocksDb*" />
      <package pattern="Microsoft.BuildXL*" />
      <package pattern="Microsoft.Windows.Debuggers*" />
    </packageSource>
  </packageSourceMapping>
</configuration>

If there is something I missed that should have prevented the need to make these changes it would be appreciated if that could be called out in the README (or maybe I missed it altogether). If these are actual errors then I'm happy to help open PRs to try and fix the issues if a repository owner has guidance on what the correct fixes are.