Propogate additional compilation data from RoslynCompilationService

* Update CompilationFailedException to include path of file being compiled
* Pass in path being compiled to Rolsyn.
* Adding doc comments for compilation pieces

Fixes #869
w.r.t. my earlier comments about `fileContent` and `compiledContent`, a small part of this, perhaps just "Gets the generated C# code that was compiled.", should be visible in the `<summary/>`.