feat: support predicted outputs in the Moonshot AI provider (#19576)

## Background

Moonshot AI consumers can provide known response content to accelerate
generation when most of the expected output is static.

## Summary

Added the optional, validated `prediction` provider option to
`MoonshotAILanguageModelOptions` and serialized string or
text-part-array content for generation and streaming requests.

## Testing

Added request tests for both prediction forms, default omission, invalid
input rejection, streaming behavior, and compile-time public type
constraints.

## End-to-end Validation

- Added and successfully ran a Moonshot AI streaming predicted-output
example against the live `kimi-k3` API.

## Documentation

Documented Moonshot AI predicted outputs, both supported content forms,
consumer usage, and the predicted-content data-sharing consideration.

## Related Issues

Fixes #19551

Co-authored-by: ai-sdk-factory <308175966+ai-sdk-factory@users.noreply.github.com>
Co-authored-by: gr2m <39992+gr2m@users.noreply.github.com>