RFR: 8310999: Add @since info in jdk.jsobject files

[Phil Race]

On Wed, 5 Jul 2023 14:51:31 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Source code cleanup.
> Add @since, remove unused imports and remove unnecessary SuppressWarnings of deprecation.

unless my eyes deceive me the suppresswarnings is still present.

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Changes requested by prr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14775#pullrequestreview-1514878528