Update Infrastructure (#961)

* Update form .NET Core 2.2 to .NET Core 3.1

- Global variable for projects
- Change TFMs from netcoreapp2.2 to netcoreapp3.1
- Update global.json
- Update build.json
- Remove direct framework cake TestCore task
- Update travis dotnet version
- Update azure pipline file
- Update vscode launch.json

* Add Central Package Management

* Fix xUnit Breaking Change for MemberData type

* Fix xUnit breaking change for duplicate test method name

* Fix Rang/Index type conflict with System.Rang/Index

* Update vscode tasks.json

* Change serviceHostExecutable path in ServiceTestDriver.cs

* Downgrade SDK version (https://github.com/appveyor/ci/issues/3440)

- Appveyor hasn't installed latest SDK therefore I downgrade it until they install it.

* Dump Microsoft.SqlServer.DACFx

src/Microsoft.SqlTools.ResourceProvider/Microsoft.SqlTools.ResourceProvider.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
+    <TargetFramework>$(ResourceProivderTargetFramework)</TargetFramework>
     <PackageId>SqlToolsResourceProviderService</PackageId>
     <AssemblyName>SqlToolsResourceProviderService</AssemblyName>
     <OutputType>Exe</OutputType>
@@ -19,8 +19,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <!-- delete reference from project once moving off preview version !-->
-    <PackageReference Include="System.Text.Encoding.CodePages" Version="4.6.0-preview3-26501-04" />
+    <PackageReference Include="System.Text.Encoding.CodePages"/>
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Microsoft.SqlTools.Hosting\Microsoft.SqlTools.Hosting.csproj" />