Detect loose paragraphs in lists

[sharwell]

Example of this error:

https://github.com/dotnet/roslyn/blob/00247a7273f1ea229d5accce18352d65f8aa6d72/src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Utilities/ReferenceCountedDisposable.cs#L42-L50

When this occurs, the paragraphs should be placed inside of <item><description>.