Support SourceLink source files (remote)

[ViktorHofer]

If using SourceLink, source file paths aren't located on the disk but on a remote endpoint. It would be sweet if ReportGenerator could support fetching files stored remotely.

cc @tonerdo @danmosemsft @jkotas

[danielpalme]

That makes sense and I'm willing to add support to it.
We only have to make sure how the path is formatted in the various output formats (e.g. Cobertura or OpenCover). Currently the path is just a file on the local disk.

[ViktorHofer]

The path in the output formats, i.e. OpenCover will look like this one: https://raw.githubusercontent.com/dotnet/coreclr/5feb0389f1e1ba715fba5560c979ac6362b1bcf8/.... It should be a normal web link. I'm open to contribute the necessary changes. Currently I'm determining with @tonerdo if changes in Coverlet are also necessary (I believe so).

[danielpalme]

Will take care of that (probably next week)

[ViktorHofer]

Thanks Daniel! Please keep me updated as we want to use that feature in corefx.

[danielpalme]

I'll let you know.

[danielpalme]

I added support for remote files in this (pre-)release:
https://www.nuget.org/packages/ReportGenerator/4.0.5-rc1
https://www.nuget.org/packages/dotnet-reportgenerator-cli/4.0.5-rc1
https://www.nuget.org/packages/dotnet-reportgenerator-globaltool/4.0.5-rc1

Let me know if this works for you.

[danielpalme]

Created global instance of HttpClient in 4.0.5-rc2

[ViktorHofer]

Changes look good to me. Thanks again!