Minor fixes to the settings schema

[ralish]

Summary of the Pull Request

Fixes a couple of minor issues in the settings schema which can result in erroneous settings validation failures.

References and Relevant Issues

None

Detailed Description of the Pull Request / Additional comments

• answerbackMessage
  Permit null type (corresponds to the default value).
• compatibility.input.forceVT
  Add missing setting (previously was experimental.input.forceVT).
• rendering.graphicsAPI
  Add missing automatic enumeration value.
• Mark several settings as deprecated using the same format and direct the user to the updated settings to use.

Validation Steps Performed

Tested updated schema against configuration with above settings present.

PR Checklist

• Schema updated (if necessary)

[carlos-zamora]

Thanks for doing this! Can you update the deprecated key below?

[ralish]

@microsoft-github-policy-service agree

[carlos-zamora]

Cross-referenced with settings model serialization code. Added a few suggestions for clarity.

Thank you so much for doing this!

[ralish]

Sorry for the extra commits but I noticed a couple of additional issues in the schema after updating to v1.23.12681. Since this isn't merged yet I've just added them in rather than open a separate PR.

The additional two commits:

• Permit null for the language settings (consistent with the default)
• Add the missing experimental.rainbowSuggestions setting (added in v1.22)

I'd also be open to performing a broader tidy-up of the settings schema as it's a bit of a mess, but that would result in a lot of churn in the diff (even if the net changes aren't necessarily significant), so I'll avoid doing that unless there's actual interest. I'm a big fan of having the JSON schema though and wish more projects adopted them for settings documentation and validation!

[DHowett]

Thanks so much for doing this! I would love for somebody to take a close look at our schema. It is often an afterthought unfortunately, and it should be a first class UI.