RFR: 8308644: [Linux] Simplify and fix small bugs on glass key related events [v4]

[Thiago Milczarek Sayao]

> While working on IME I noticed this code could be simplified, so I removed the `g_hash_table` usage for a simple struct ordered for binary search (I'm sure it's ordered because I did a simple app to generate it ordered).
> 
> This also fixes:
> 
> - UNKNOWN key codes being sent on KEY_PRESS;
> - Alt Gr is now working;
> - Replaced X calls with GDK calls for key locked check for as a small step towards supporting Wayland in the future
> - Added missing mappings (for F13 - F24 and dead keys) - Linux does not send dead keys as keypress but sends as key release, and they might be used on a robot test, so it's now covered.

Thiago Milczarek Sayao has updated the pull request incrementally with two additional commits since the last revision:

 - Forgot test code
 - Back to hash

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1143/files
  - new: https://git.openjdk.org/jfx/pull/1143/files/49165bf2..06968167

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1143&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1143&range=02-03

  Stats: 428 lines in 2 files changed: 210 ins; 193 del; 25 mod
  Patch: https://git.openjdk.org/jfx/pull/1143.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1143/head:pull/1143

PR: https://git.openjdk.org/jfx/pull/1143