[Razor] Bring back RazorLangversion 6.0

[javiercn]

We undid the change for adding a new RazorLangVersion because we thought it would resolve some build/stability issues that we were observing on the build. Undoing the change didn't seem to fix the issue, so we should try and bring back the change and solve the underlying root cause.

This issue tracks the work for "re-reverting the commits" on the SDK and the razor compiler as well as updating the codebase in all places where its necessary to key off functionality of RazorLangVersion 6.0:

• Generic type constraints
• Generic parameters type inference
• JS Modules

[captainsafia]

@javiercn We can do this once #32581 is in which attempts to resolve the generic params issue by disabling the RSG for projects where it is throwing errors.

EDIT: Actually, we don't need to wait for that PR. We can do it in parallel.

[javiercn]

@captainsafia If you want to do it, go ahead.

I don't think we have any rush to bump the version, just filed an issue to make sure we keep track of it and have a place to put all the things we need to key of of this.

[captainsafia]

Now that we're on the new SDK, let's give it a couple of days to see how things fare with the build issues.

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).
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