Support ARM64 WSL on ARM64 devices

[nathansoz]

Issue Description

Would like to use x86 VSCode on my SPX as a frontend to dotnet running on WSL (ARM64). When I try to install the extension I get two errors:

Starting OmniSharp server at 1/29/2020, 11:49:28 AM
    Target: <snip>

[ERROR] Error: spawn /home/nsosnov/.vscode-server/extensions/ms-vscode.csharp-1.21.9/.omnisharp/1.34.9/run ENOENT

And

[WARNING]: Processor architecture 'aarch64' is not currently supported by the .NET Core debugger. Debugging will not be available.

I thought I have seen issues on github indicating that ARM64 is now supported by the .net core debugger (#2105). There looks to be some manual configuration pointed to, but it isn't clear to me that doing this would actually unblock omnisharp.

Steps to Reproduce

Use the WSL remote extension on an ARM64 device and attempt to open a c# project. See errors as above.

Expected Behavior

The c# debugger should download and omnisharp should start up properly.

Actual Behavior

Omnisharp does not start.

Logs

OmniSharp log

Starting OmniSharp server at 1/29/2020, 11:49:28 AM Target:

[ERROR] Error: spawn /home/nsosnov/.vscode-server/extensions/ms-vscode.csharp-1.21.9/.omnisharp/1.34.9/run ENOENT

C# log

[WARNING]: Processor architecture 'aarch64' is not currently supported by the .NET Core debugger. Debugging will not be available.

Environment information

VSCode version: 1.41.1
C# Extension: 1.21.9

Mono Information

OmniSharp using built-in mono

Dotnet Information

.NET Core SDK (reflecting any global.json): Version: 3.1.101 Commit: b377529961

Runtime Environment:
OS Name: ubuntu
OS Version: 18.04
OS Platform: Linux
RID: ubuntu.18.04-arm64
Base Path: /home/nsosnov/dotnet/sdk/3.1.101/

Host (useful for support):
Version: 3.1.1
Commit: a1388f194c

.NET Core SDKs installed:
3.1.101 [/home/nsosnov/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.App 3.1.1 [/home/nsosnov/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.1 [/home/nsosnov/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
csharp	ms-vscode	1.21.9
docomment	k--kato	0.1.8
dotnet-test-explorer	formulahendry	0.7.1

[gregg-miskelly]

I think this is really just a special case for #2771, so we don't need a separate issue.

[nathansoz]

Sounds good.