RFR: 8280031: Deprecate GTK2 for removal

[Phil Race]

On Fri, 5 May 2023 15:21:14 GMT, Alexander Zvegintsev <azvegint at openjdk.org> wrote:

> GTK3 has been the default for several years now. GTK2 is now only available by specifying it with the jdk.gtk.version system property. With the announcement of the GTK 4 release in December 2020, the GTK 2 toolkit has reached its end of life.
> 
> It is time to deprecate it for removal.
> 
> Since there's no associated API, we just print a deprecation message once when trying to load gtk2.
> 
> CSR: https://bugs.openjdk.org/browse/JDK-8307481

Marked as reviewed by prr (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/13834#pullrequestreview-1415184242