[Rev 25] RFR: 8236651: Simplify and update glass gtk backend

[Thiago Milczarek Sayao]

> This proposed change does the following:
> 
> - Ports DND target to use GTK reducing code size and adding extra text / image formats (such as .gif);
> - Use gtk signals instead of gdk events (also to reduce code size);
> - Simplifies geometry (sizing/positioning) with a more straightforward code (less special cases), making it easier to understand and maintain;
> - Replaces (pointer and focus) grabbing with a gtk approach;
> - Reworked frame extents (the wm extension to get decoration sizes) to reduce size and complexity;
> - Simplified cursor changing (for gtk3);
> - Reduced the use of gtk/gdk deprecated functions;
> - Removes Applet/Web Start code;
> - Fixes https://bugs.openjdk.java.net/browse/JDK-8237491;
> 
> In general it reduces code size and complexity and hands more work to gtk.
> 
> Updated on 2020-01-29:
> ![image](https://user-images.githubusercontent.com/30704286/73354728-2ce47d00-4275-11ea-935c-414fc26163d7.png)

The pull request has been updated with a new target base due to a merge or a rebase.

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

Commits:
 - f772c2e7: Merge branch 'master' into jdk_8236651
 - 37519d74: Merge pull request #5 from openjdk/master
 - 08caafd9: Remove unused var
 - 2c51b045: Fix pointer grab bug
 - 2e3ce44a: Ajustments
 - 06968c9d: Fix bug on extents calculation
 - 84bfd8b8: Fix POPUP window positioning
 - 465c9cdd: Fix seat_grab param
 - 7ed26f41: Revert back focus mechanism
 - 22c38d7f: Merge branch 'jdk_8236651' of https://github.com/tsayao/jfx into jdk_8236651
 - 14a75ce4: Merge branch 'master' into jdk_8236651
 - e829b8e9: Better fix for initial size
 - 058a0992: Revert "Fix Initial Size"
 - 0c982d60: Fix Initial Size
 - 2d10fe8c: Merge branch 'jdk_8236651' of https://github.com/tsayao/jfx into jdk_8236651
 - 694641f6: JDK-8236651 Simplify and update glass gtk backend
 - 9397a748: Merge pull request #4 from openjdk/master
 - cb2d9fb6: Work on mouse grab
 - 2bfac077: Mouse pointer grab
 - 4b555624: Allow undecorated windows to be maximized.
 - f35fa9b1: Big cleanup
 - f99aebcf: Maybe fix background
 - 9850bb71: Fix dialog with owner sizing
 - 209b7ac7: Better alternative calculation for no _NET_FRAME_EXTENTS WM extension
 - 0dc70ab3: Use gtk_window_set_default_size for before-map sizing which is the appropriate function
 - e4d2a1d2: Small fixes
 - cc7745b4: Pass more tests
 - 49426b66: Fix flickering and sizing issues
 - 628d5528: Revert idea files
 - 8b0cadfc: Fix crash
 - 1c3df122: Fix crash
 - 4691800a: Fix crash
 - 7b48e484: Cleaning + change year to 2020
 - 039daa4a: Cleaning
 - 9f209f1e: JDK-8236651 Simplify and update glass gtk backend

Changes: https://git.openjdk.java.net/jfx/pull/77/files
 Webrev: https://webrevs.openjdk.java.net/jfx/77/webrev.25
  Stats: 3343 lines in 12 files changed: 773 ins; 1774 del; 796 mod
  Patch: https://git.openjdk.java.net/jfx/pull/77.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/77/head:pull/77

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