Trying to install wasi-experimental workload doesn't work if dotnet is installed via snap

[jdetter]

On Ubuntu if you install dotnet using snap, then you will get this error when you try to install the wasi-experimental workload:

> sudo dotnet workload install wasi-experimental
Unhandled exception: System.IO.IOException: Read-only file system : '/snap/dotnet-sdk/245/metadata'
   at System.IO.FileSystem.CreateDirectory(String fullPath, UnixFileMode unixCreateMode)
   at System.IO.Directory.CreateDirectory(String path)
   at Microsoft.DotNet.Workloads.Workload.Install.WorkloadInstallerFactory.CanWriteToDotnetRoot(String dotnetDir)
   at Microsoft.DotNet.Workloads.Workload.Install.WorkloadInstallerFactory.GetWorkloadInstaller(IReporter reporter, SdkFeatureBand sdkFeatureBand, IWorkloadResolver workloadResolver, VerbosityOptions verbosity, String userProfileDir, Boolean verifySignatures, INuGetPackageDownloader nugetPackageDownloader, String dotnetDir, String tempDirPath, PackageSourceLocation packageSourceLocation, RestoreActionConfig restoreActionConfig, Boolean elevationRequired, Boolean shouldLog)
   at Microsoft.DotNet.Workloads.Workload.Install.WorkloadInstallCommand..ctor(ParseResult parseResult, IReporter reporter, IWorkloadResolverFactory workloadResolverFactory, IInstaller workloadInstaller, INuGetPackageDownloader nugetPackageDownloader, IWorkloadManifestUpdater workloadManifestUpdater, String tempDirPath, IReadOnlyCollection`1 workloadIds)
   at Microsoft.DotNet.Cli.WorkloadInstallCommandParser.<>c.<ConstructCommand>b__6_0(ParseResult parseResult)
   at System.CommandLine.Invocation.InvocationPipeline.Invoke(ParseResult parseResult)
   at Microsoft.DotNet.Cli.Program.ProcessArgs(String[] args, TimeSpan startupTime, ITelemetry telemetryClient)

IMO we should at least improve the error message for users when they hit this because its not immediately clear its because of snap.