RFR: 8305418: [Linux] Replace obsolete XIM as Input Method Editor [v3]

[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 03-09-2023 19:10:36.webm](https://github.com/openjdk/jfx/assets/30704286/2a36e9d0-59be-4092-905f-e31fabc6e2e4)

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

  begin to use pango_attrs

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1080/files
  - new: https://git.openjdk.org/jfx/pull/1080/files/7bbfa914..6bbecc15

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1080&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1080&range=01-02

  Stats: 71 lines in 4 files changed: 26 ins; 24 del; 21 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