RFR: 8271398: GTK3 drag view image swaps red and blue color channels [v2]

[Thiago Milczarek Sayao]

> It seems raw images need to be converted BRGA -> RGBA.
> 
> It was being converted on gtk2 code path, but gtk3 only uses `gtk_drag_set_icon_pixbuf`.
> 
> I have simplified the gtk2 `DragView::View::expose` to paint with `gdk_cairo_set_source_pixbuf` (that is available since Gtk 2.8) because the old way was somehow converting  again.
> 
> Run the issue sample with `-Djdk.gtk.version=2` to test the gtk2 code path.
> 
> To test:
> 
> `./gradlew apps`
> 
> 
> java @build/run.args -cp apps/toys/DragDrop/dist/DragDrop.jar dragdrop.DragDropWithControls
> java @build/run.args -cp apps/toys/DragDrop/dist/DragDrop.jar dragdrop.DragDropColor 
> 
> java -Djdk.gtk.version=2 @build/run.args -cp apps/toys/DragDrop/dist/DragDrop.jar dragdrop.DragDropWithControls
> java -Djdk.gtk.version=2 @build/run.args -cp apps/toys/DragDrop/dist/DragDrop.jar dragdrop.DragDropColor

Thiago Milczarek Sayao has updated the pull request incrementally with one additional commit since the last revision:

  Provide test

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/599/files
  - new: https://git.openjdk.java.net/jfx/pull/599/files/de2d8ddc..5530488c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=599&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=599&range=00-01

  Stats: 171 lines in 1 file changed: 171 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/599.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/599/head:pull/599

PR: https://git.openjdk.java.net/jfx/pull/599