Unix (MacOS / Linux) support for Blazor demos

[manfromarce]

I've tried to run the Blazor Server demo on Linux, but an exception occurs because the ChromelyBlazor.Shared project uses MemoryMappedFile with names, which are not supported on Unix systems. It would be nice if this was changed.

[andrew-bedford]

While named memory maps are not supported on Linux, anonymous ones apparently are. I was able to get it running on Linux by changing the calls from MemoryMappedFile.CreateNew(appName, 4) to MemoryMappedFile.CreateNew(null, 4) and changing MemoryMappedFile.CreateOrOpen(appName, 4) to MemoryMappedFile.CreateNew(null, 4). I don't think it's the right solution though, so I wouldn't commit it.