Add an option to search for projects in subdirectories as well

It would be great if we could leverage slngen to keep our solution files up-to-date dotnet/runtime in which we have the following project hierarchy:

- System.Runtime.Serialization.Formatters
  - ref
      System.Runtime.Serialization.Formatters.csproj
  - src
      System.Runtime.Serialization.Formatters.csproj
  - tests
      System.Runtime.Serialization.Formatters.Tests.csproj

By default slngen only searches for project files in the current directory if one isn’t specified. Can we change this so that it searches for project files in subdirectories as well either by default or under a switch?

Note that we would probably need multiple entry points here as we don’t have a clear dependency chain yet between ref, src and test projects.

cc @jeffkl

[jeffkl]

Recent versions of SlnGen support this by specifying a globbing pattern like **\*.csproj. You can also exclude globs with:

slngen **\*.csproj --exclude:"**\*Test.csproj

For more advanced scenarios like mapping globs to solution folders, let’s open a new issue to track that.

[michael-hawker]

Globbing (**\*.csproj) seems to work well here, though there’s no option to configure the structure of solution itself. It just uses the folder structure if you use the existing --folder true --collapsedfolders true settings.