Correctly handle multiple reference aliases

[laenas]

The element of a or supports multiple aliases. Currently, OmniSharp will flag attempted usings of these aliases as errors, despite the fact that they are valid and the project will still build without issue.
I can find no hard documentation of this specification, but have manually tested to confirm the three primary points of this PR:

1. Multiple aliases are supported
2. They are comma separated (semicolons trigger build errors)
3. They are insensitive to both leading and trailing whitespace.

[dnfadmin]

All CLA requirements met.

[david-driscoll]

I wonder if both , and ; are supported here, I'm not able to find much documentation however.

[laenas]

They are not - in the case that the element contains a semicolon-separated list of aliases, the build process will fail:

Roslyn\Microsoft.CSharp.Core.targets(70,5): error MSB6001: Invalid command line switch for "csc.dll". System.ArgumentException: MSB3053: The assembly alias "abc;def" on reference

[laenas]

For reference:
https://github.com/dotnet/roslyn/blob/e261d15d5546f3a96a2226faf35adffc53098395/src/Compilers/Core/MSBuildTask/Csc.cs#L335

[filipw]

maybe just write it in one line

!string.IsNullOrWhiteSpace(projectReferenceAliases)
                ? ImmutableArray.CreateRange(projectReferenceAliases.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries).Select(a => a.Trim()))
                : ImmutableArray<string>.Empty;

this is exactly what Roslyn uses internally

[laenas]

Done - I erred on the side of trying to avoid LINQ for performance, but I do suppose this isn't directly in the hotpath.

[filipw]

LGTM

[filipw]

@david-driscoll what do you think?

[david-driscoll]

Seems good to me!