RFR: 8300868: Reduce visibility in java.io.SerialCallbackContext [v2]

[Roger Riggs]

On Mon, 23 Jan 2023 15:36:01 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to reduce the visibility for constructor and methods in `java.io.SerialCallbackContext`.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update copyright year

Its a package private class, not really a significant change.

-------------

Marked as reviewed by rriggs (Reviewer).

PR: https://git.openjdk.org/jdk/pull/12143