Remove reliance on preview LanguageVersion for incremental RSG

[captainsafia]

The incremental RSG currently requires a preview language version. We'll need to remove this once the compiler supports it.

[ghost]

Thanks for contacting us.

We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[pranavkm]

Resolved as part of dotnet/sdk#18817

[captainsafia]

@pranavkm Actually no. I had to revert because the incremental API still depends on the preview version. Confirmed the behavior with Chris last week.

[pranavkm]

Clearing the milestone so we can bring this up for triage. We want to fix this for rc1.

[mkArtakMSFT]

@pranavkm what is left here given that your PRs were already merged in the SDK repo?