Bump target frameworks of C# programs from netcoreapp1.0 to netcoreapp2.1 (#5838)
* Bump target frameworks from netcoreapp1.0 to netcoreapp2.2.
Move global.json up to root of repo, change SDK ver to 2.2.100
Change .net core sdk in dockerfile for kokoro to ver 2.2.100
* Re-add curl install
* Change all exe target to 2.1
* Fix incorrect versions in global.json and Dockerfile
* Downgrade version to 2.1 to match exe targets
* introduce separate testing Dockerfile for C#
* revert changes to the shared Dockerfile
* use netcoreapp2.1 for C# conformance tests
* use language specific dockerfile for testing C#
* Edit compatibility tests script to use parameters instead of file copies
* install dotnet SDK on windows before running the tests
* update csharp_EXTRA_DIST
diff --git a/csharp/install_dotnet_sdk.ps1 b/csharp/install_dotnet_sdk.ps1
new file mode 100644
index 0000000..b4132ab
--- /dev/null
+++ b/csharp/install_dotnet_sdk.ps1
@@ -0,0 +1,21 @@
+#!/usr/bin/env powershell
+# Install dotnet SDK based on the SDK version from global.json
+
+Set-StrictMode -Version 2
+$ErrorActionPreference = 'Stop'
+
+# avoid "Unknown error on a send" in Invoke-WebRequest
+[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
+
+$InstallScriptUrl = 'https://dot.net/v1/dotnet-install.ps1'
+$InstallScriptPath = Join-Path "$env:TEMP" 'dotnet-install.ps1'
+$GlobalJsonPath = Join-Path $PSScriptRoot '..' | Join-Path -ChildPath 'global.json'
+
+# Resolve SDK version from global.json file
+$GlobalJson = Get-Content -Raw $GlobalJsonPath | ConvertFrom-Json
+$SDKVersion = $GlobalJson.sdk.version
+
+# Download install script
+Write-Host "Downloading install script: $InstallScriptUrl => $InstallScriptPath"
+Invoke-WebRequest -Uri $InstallScriptUrl -OutFile $InstallScriptPath
+&$InstallScriptPath -Version $SDKVersion
