RFR: 8236651: Simplify and update glass gtk backend

[Tor (torbuntu)]

On Wed, 29 Jul 2020 20:46:16 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> Would it be possible and related to add the gtk touch events to this PR as part of the Glass GTK3 update? Or would  follow up update PR adding that be more appropriate? 
>> 
>> Currently linux desktop does not have touch support because of the missing gesture/touch events from gtk3.
>
> @Torbuntu Not to this PR, I don't want to delay it too much. But can be done (I just do not own a touch device currently).

Sounds good! I have a few devices I'd be more than excited to test on, and even help add the feature myself if I can figure it out if time is a big issue?

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PR: https://git.openjdk.java.net/jfx/pull/77