GetInsertionIndex should include the entry's name when it throws an InvalidOperationException

[wilbaker]

While on support I found that this error did not include any information about the entry that VFS4G determined was non-unique:

[2/15/2019 12:13:36 PM] Error {"Area":"GitIndexProjection",
"Exception":"System.InvalidOperationException: All entries should be unique
   at GVFS.Virtualization.Projection.GitIndexProjection.SortedFolderEntries.GetInsertionIndex(LazyUTF8String name)
   at GVFS.Virtualization.Projection.GitIndexProjection.AddItemFromIndexEntry(GitIndexEntry indexEntry)
   at GVFS.Virtualization.Projection.GitIndexProjection.GitIndexParser.AddToProjection(GitIndexEntry data)
   at GVFS.Virtualization.Projection.GitIndexProjection.GitIndexParser.ParseIndex(ITracer tracer, Stream indexStream, Func`2 entryAction)
   at GVFS.Virtualization.Projection.GitIndexProjection.GitIndexParser.RebuildProjection(ITracer tracer, Stream indexStream)
   at GVFS.Virtualization.Projection.GitIndexProjection.BuildProjection()
   at GVFS.Virtualization.Projection.GitIndexProjection.ParseIndexThreadMain()",
"ErrorMessage":"ParseIndexThreadMain caught unhandled exception, exiting process"}

With the changes in this PR, the item's name will be included in the exception message:

"Exception":"System.InvalidOperationException: All entries should be unique, non-unique entry: Params.cpp

Although the full path is not included, having the file name helps when tracking down which entries in the index might be causing an issue.

[jrbriggs]

Thanks for this!