[Rev 19] 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 21 additional commits.

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

Added commits:
 - 7ed26f41: Revert back focus mechanism
 - 22c38d7f: Merge branch 'jdk_8236651' of https://github.com/tsayao/jfx into jdk_8236651
 - 2d10fe8c: Merge branch 'jdk_8236651' of https://github.com/tsayao/jfx into jdk_8236651
 - 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:
  - all: https://git.openjdk.java.net/jfx/pull/77/files
  - new: https://git.openjdk.java.net/jfx/pull/77/files/14a75ce4..7ed26f41

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/77/webrev.19
 - incr: https://webrevs.openjdk.java.net/jfx/77/webrev.18-19

  Stats: 65 lines in 2 files changed: 17 ins; 24 del; 24 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