Support title schema property in completion items

[NotWearingPants]

Currently jsonCompletion.ts returns CompletionItems with their documentation property set to the value of description or markdownDescription from the JSON schema, which VSCode then displays as a popup next to the list of completions:

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VSCode also let's completions control a short description shown right in the completions list, e.g. in JS:

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This text is fetched from the CompletionItem's detail property (from the LSP spec).

JSON schema supports both a description and a title field (JSON schema spec) for such UI purposes.

Can you pass titles from the schema to details in completion items?