ensure path casing for debug documents

[ctaggart]

While enabling source link for Rx.NET #167, we discovered that calling the PowerShell build scripts with the wrong case resulted in debug documents with wrong case for the paths too. My guess is that the full path msbuild call is resulting in a compiler property. To make enabling source link easier, we should investigate and see if it is possible to override with a Path.GetFullPath or something similar.

[ctaggart]

The solution for this one should hopefully be pretty easy. In the SourceLink.Create.GitHub.targets, we just need to change it to pass in both @(Compile) and @(EmbeddedFiles), then also pass back out @(Compile) with Path.GetFullPath called called for each item.

[ctaggart]

This affects SourceLink.Create.GitHub and not SourceLink.Create.CommandLine. Rx.NET has switched to Rx.NET. I'm going to close this until it is surfaces again.