RFR: 8308644: [Linux] Simplify and fix small bugs on glass key related events [v5]

[Thiago Milczarek Sayao]

> This PR adds missing key mappings, fixes "Alt Gr" for some systems and cleans `process_key`a little bit.

Thiago Milczarek Sayao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 16 additional commits since the last revision:

 - Minimize changes
 - Merge branch 'master' into gdk_to_glass_key_map
 - Forgot test code
 - Back to hash
 - Revert key lock change because it has different behaviour
 - Revert modifier change + Remove F13 -> F24
 - Remove print statement
 - Use GDK instead of X calls (to ease in a future wayland implementation)
 - Avoid sending unknown key event
 - GDK_META_MASK is not ALT
 - ... and 6 more: https://git.openjdk.org/jfx/compare/af7d366c...aad021a6

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1143/files
  - new: https://git.openjdk.org/jfx/pull/1143/files/06968167..aad021a6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1143&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1143&range=03-04

  Stats: 40615 lines in 878 files changed: 12420 ins; 3782 del; 24413 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