RFR: universal type variables: initial prototype [v4]

[Vicente Romero]

On Thu, 12 Aug 2021 17:53:14 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> First iteration of the protype for universal type variables
>
> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comments, another iteration

thanks for the review

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PR: https://git.openjdk.java.net/valhalla/pull/521