Use `field` keyword on generated relay commands

[colejohnson66]

Overview

If LangVersion=preview, the relay command generator should avoid emitting a backing field.

API breakdown

N/A

Usage example

N/A

Breaking change?

No

Alternatives

N/A

Additional context

No response

Help us help you

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[weitzhandler]

Yes please. These fields are added to the accessible private fields in the view-model and are visible in intellisense. They're redundant and confusing.

In any case (even LangVersion < 14) these fields should be hidden from intellisense.