RFR: 8305418: [Linux] Replace obsolete XIM as Input Method Editor [v29]

[Thiago Milczarek Sayao]

> This replaces obsolete XIM and uses gtk api for IME.
> Gtk uses [ibus](https://github.com/ibus/ibus)
> 
> Gtk3+ uses relative positioning (as Wayland does), so I've added a Relative positioning on `InputMethodRequest`.
> 
> [Screencast from 17-09-2023 21:59:04.webm](https://github.com/openjdk/jfx/assets/30704286/6c398e39-55a3-4420-86a2-beff07b549d3)

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

  Set IBUS_ENABLE_SYNC_MODE=1

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1080/files
  - new: https://git.openjdk.org/jfx/pull/1080/files/7d8e5bcc..8eccd986

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1080&range=28
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1080&range=27-28

  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1080.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1080/head:pull/1080

PR: https://git.openjdk.org/jfx/pull/1080