Feature: Schema editing support for localSchemaFile

[Cellule]

Originally from: #247

When working with localSchemaFile it would be nice to have minimal schema editing features.

Here's a few ideas that comes to mind

• "Go to Definition" when hovering on a field's type
• Basic validation like showing an error when the type of a field is unknown
• Autocomplete when typing a field's type

As mentioned in the original issue, maybe having a rover config would help, but I'd still love some support considering the extension has all the necessary schema information to provide an improved developer experience
https://www.apollographql.com/docs/graphos/schema-design/connectors/vs-code

For reference in https://marketplace.visualstudio.com/items?itemName=GraphQL.vscode-graphql
I get type validation, type information on hover and go to definition

[dylanwulf]

I agree with this, I would at least like to have "Go to definition" working on a local schema file without requiring rover