Fixes #388

This PR changes the behaviour of the --upgrade command to preserve the max version specified in a package reference, e.g. <PackageReference Include="Microsoft.AspNetCore.Authentication.Negotiate" Version="[6.0.13,7)" />.

For example, upgrading a project with would change the version of Microsoft.AspNetCore.Authentication.Negotiate in the csproj from/to:
[6.0.13,7) -> [6.0.36, 7.0.0)
[6.0.13,7] -> [7.0.0]
[6.0.13] -> "No outdated dependencies were detected", as the version is pinned
[6.0.13,) -> 8.0.24
6.0.13 -> 8.0.24
6.* -> 8.0.24
[6.*, 8) -> [7.0.20, 8.0.0)

Note that this does not preserve "floating" versions like 6.*.

However, if the new version is outside the the declared version range (which can happen due to #670), then we remove the maximum version to avoid setting an unsatisfiable version range. e.g. when running dotnet outdated -u -mv 8.0, [6.0.13,7) is updated to 8.0.24 instead of [8.0.24, 7.0.0).