RFR: 8236651: Simplify and update glass gtk backend

[Thiago Milczarek Sayao]

On Wed, 10 Jun 2020 02:25:00 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> I am running a full test using GTK 3 on Ubuntu 20.04 and will publish results. I will later do the same for Oracle Linux 7.7.
>> 
>> One thing to note is that this new GTK pipeline doesn't run on Ubuntu 16.04. I get the following running any program:
>> 
>> $ java -Djavafx.gtk.experimental=true -Djdk.gtk.verbose=true HelloRectangle
>> checking GTK version 3
>> trying GTK library libgtk-3.so.0
>> using GTK library version 3 set libgtk-3.so.0
>> Glass GTK library to load is glassgtk3_exp
>> loaded gdk_x11_display_set_window_scale
>> java: symbol lookup error: /localhome/kcr/javafx/jfx-tmp/jfx/rt/build/sdk/lib/libglassgtk3_exp.so: undefined symbol: gdk_display_get_n_monitors
>
>> I am running a full test using GTK 3 on Ubuntu 20.04 and will publish results. I will later do the same for Oracle Linux 7.7.
>> 
>> One thing to note is that this new GTK pipeline doesn't run on Ubuntu 16.04. I get the following running any program:
>> 
>> ```
>> $ java -Djavafx.gtk.experimental=true -Djdk.gtk.verbose=true HelloRectangle
>> checking GTK version 3
>> trying GTK library libgtk-3.so.0
>> using GTK library version 3 set libgtk-3.so.0
>> Glass GTK library to load is glassgtk3_exp
>> loaded gdk_x11_display_set_window_scale
>> java: symbol lookup error: /localhome/kcr/javafx/jfx-tmp/jfx/rt/build/sdk/lib/libglassgtk3_exp.so: undefined symbol: gdk_display_get_n_monitors
>> ```
> 
> I have limited GTK compilation to use GTK 3.8 symbols. Will run more tests, but should fix it.

Here is the result on Ubuntu 20.04 with the latest changes:

![image](https://user-images.githubusercontent.com/30704286/84271590-abdea180-ab02-11ea-9d2d-dbca39755db0.png)

Some tests seems intermittent.

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