RFR: 8273379 - GTK3 stops sending key events during drag and drop [v15]

[Thiago Milczarek Sayao]

> This PR fixes 8273379.
> 
> I reverted back to use GDK (from [8225571](https://bugs.openjdk.org/browse/JDK-8225571)) to handle the events. 
> 
> It may also fix [8280383](https://bugs.openjdk.org/browse/JDK-8280383).
> 
> There's also some cleaup.
> 
> The most changed part is that I had to move `process_events` to `glass_evloop`  because it's reused in glass_dnd.
> 
> To do general testing:
> `java @build/run.args -jar apps/toys/DragDrop/dist/DragDrop.jar`

Thiago Milczarek Sayao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 47 additional commits since the last revision:

 - Rework
 - Rework events
 - Merge branch 'master' into 8273379-dnd-keys
 - Merge branch 'openjdk:master' into master
 - Device Grab Work
 - Adjustments
 - Replace g_warning
 - Improvements
 - Add test
 - Add testing
 - ... and 37 more: https://git.openjdk.org/jfx/compare/89f8ac54...f916a108

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/986/files
  - new: https://git.openjdk.org/jfx/pull/986/files/08d05af8..f916a108

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=986&range=14
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=986&range=13-14

  Stats: 4806 lines in 81 files changed: 3541 ins; 825 del; 440 mod
  Patch: https://git.openjdk.org/jfx/pull/986.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/986/head:pull/986

PR: https://git.openjdk.org/jfx/pull/986