Intellisense for Serverless.Template Json File In Visual Studio (.Net Core)

When I add a Serverless Application and try to use an output parameter from that stack in the parent stack, Intellisense complains as an invalid key for this object, but it works fine when I deploy it.

Parent template:
`{`
` "AWSTemplateFormatVersion" : "2010-09-09",`
` "Transform" : "AWS::Serverless-2016-10-31",`
` "Resources" : { `
` "NestedStack" : {`
` "Type" : "AWS::Serverless::Application",`
` "Properties" : {`
` "Location" : "./serverless_nested.template"`
` }`
` }`
` },`
` "Outputs" : {`
` "NestedStackOutput" : {`
` "Value" : {"Fn::GetAtt" : [ "NestedStack", "Outputs.ApplicationOutputName"]}`
` }`
` }`
`}`

Nested template:

`{`
` "AWSTemplateFormatVersion" : "2010-09-09",`
` "Transform" : "AWS::Serverless-2016-10-31",`
` "Resources" : {`
` "OrdersTable" : {`
` "Type" : "AWS::Serverless::SimpleTable",`
` "Properties" : {`
` "TableName" : "Order",`
` "PrimaryKey" : {`
` "Name" : "Id",`
` "Type" : "Number"`
` },`
` "ProvisionedThroughput" : {`
` "ReadCapacityUnits" : 5,`
` "WriteCapacityUnits" : 5`
` }`
` }`
` }`
` },`
` "Outputs" : {`
` "ApplicationOutputName" : {`
` "Value" : { "Ref" : "OrdersTable" }`
` }`
` }`
`}`

## Expected Behavior
Intellisense was to accept this content.

## Current Behavior
Intellisense underline and colour the tag in red and shows a hint saying "Outputs.ApplicationOutputName is an unknown attribute for this resource".

## Possible Solution
I had a similar problem in the past ( #1191 ) and that was fixed by "updating the backing schema for the editor".

## Your Environment

* AWSSDK.Core version used: AWSToolsAndSDKForNet_sdk-3.3.529.0_ps-3.3.522.0_tk-1.14.5.0
* Operating System and version: Windows 10 Pro 10.0.18362 N/A Build 18362
* Visual Studio version: 2019 16.1.2
* Targeted .NET platform: 2.1.10
* AWS Toolkit for Visual Studio 2017 1.15.2.0

[logging]: http://docs.aws.amazon.com/sdk-for-net/v3/developer-guide/net-dg-config-other.html

No repository file or test is named. Reproduce the warning with the parent and nested Serverless template examples in the issue, then trace the Visual Studio editor's backing schema; done means the Outputs.ApplicationOutputName attribute is accepted without an unknown-attribute warning.

Written by the indexing model from the issue text.