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

.vscode/launch.json

@@ -10,7 +10,7 @@
             "request": "launch",
             "preLaunchTask": "build",
             // If you have changed target frameworks, make sure to update the program path.
-            "program": "${workspaceFolder}/src/Microsoft.SqlTools.ServiceLayer/bin/Debug/netcoreapp2.2/MicrosoftSqlToolsServiceLayer.dll",
+            "program": "${workspaceFolder}/src/Microsoft.SqlTools.ServiceLayer/bin/Debug/netcoreapp3.1/MicrosoftSqlToolsServiceLayer.dll",
             "args": [],
             "cwd": "${workspaceFolder}/src/Microsoft.SqlTools.ServiceLayer",
             // For more information about the 'console' field, see https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md#console-terminal-window

.vscode/tasks.json

@@ -7,7 +7,7 @@
             "type": "process",
             "args": [
                 "build",
-                "${workspaceFolder}/test/Microsoft.SqlTools.ServiceLayer.IntegrationTests/Microsoft.SqlTools.ServiceLayer.IntegrationTests.csproj"
+                "${workspaceFolder}/sqltoolsservice.sln"
             ],
             "problemMatcher": "$msCompile"
         }