[Breaking change]: dotnet sln add

[edvilme]

Description

dotnet/sdk#44570
Starting in 9.0.2xx, the cli command dotnet sln add will add support for .slnx solution files using the new vs-solutionpersistence serializer.
As a result, slight changes in behavior are expected.

Version

Other (please put exact version in description textbox)

Previous behavior

• Projects and Solution Folders could have invalid Windows filenames, or invalid characters in their names
• Command would fail when attempting to add a nested project with the same name as an existing project

New behavior

• Projects and Solution Folders names cannot be a DOS word: NUL, CON, AUX, PRN, COM?, LPT?. CLOCK$ (where ? is any number of digits)
• Projects and Solution Folder names cannot be more than 260 characters
• Projects and Solution Folder names cannot contain invalid characters such as control characters or ? : \ / * " " < > |
• Command will no longer fail when attempting to add a nested project with the same name as an existing project, mimicking behavior for non-nested projects.
  Example, adding foo/bar.csproj and parent/child/bar.csproj will not result in an error
• Exceptions will contain the current strings, but will wrap vs-solutionpersistence's error messages

Type of breaking change

• Binary incompatible: Existing binaries might encounter a breaking change in behavior, such as failure to load or execute, and if so, require recompilation.
• Source incompatible: When recompiled using the new SDK or component or to target the new runtime, existing source code might require source changes to compile successfully.
• Behavioral change: Existing binaries might behave differently at run time.

Reason for change

This changes are introduced for transitioning to the new vs-solutionpersistence serializer

Recommended action

Review project and solution folders names

Feature area

SDK

Affected APIs

AddProjectToSolutionCommand.Execute

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Associated WorkItem - 351645