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

[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`.

It simplified the gtk2 `DragView::View::expose` to paint with `gdk_cairo_set_source_pixbuf` (that is available since Gtk 2.8). The  existing path seems to be converting again.

Run the issue sample with `-Djdk.gtk.version=2` to test.

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

Commit messages:
 - Fix JDK-8271398
 - Merge branch 'openjdk:master' into master
 - Merge branch 'openjdk:master' into master
 - Merge pull request #18 from openjdk/master
 - Merge pull request #17 from openjdk/master
 - Merge pull request #16 from openjdk/master
 - Merge pull request #15 from openjdk/master
 - Merge pull request #14 from openjdk/master
 - Merge pull request #13 from openjdk/master
 - Merge pull request #12 from openjdk/master
 - ... and 8 more: https://git.openjdk.java.net/jfx/compare/ba61a173...de2d8ddc

Changes: https://git.openjdk.java.net/jfx/pull/599/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=599&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271398
  Stats: 24 lines in 1 file changed: 5 ins; 18 del; 1 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