* WIP support solution folders for dotnet add and remove
* Add/remove solution folders based on directory hierarchy
* Fix tests
* Disable the solution building tests
* Address PR comments
* Fix a build break due to a new tool version used in the build
* Create SlnProjectExtensions and SlnProjectCollectionExtensions per PR comments
* WIP Improve sln migration tests
* Simple migration test
* Improve the test
* WIP update test assets
* Update test
* Test a bug fix
* Add another migrate sln test
* Fix FilePath related tests
* Finish the migrate sln tests
* Fix tests
* Fix another path issue