NEWS: update to FlatLaf 3.5.4

[Makarius]

*** Isabelle/jEdit Prover IDE ***

* Update to FlatLaf 3.5.4, the latest release. 2.6 was the last portable
version, but 3.x requires a Java jar together with a native library. The
latter is missing for arm64-linux, so old 2.6 is used on that platform:
this may lead to minor differences in GUI appearance and behaviour.

* Due to the update of FlatLaf, x86_64-linux with Wayland window manager
(e.g. standard Ubuntu) now renders submenus like "File / Recent Files"
properly. On arm64-linux an old problem of FlatLaf persists, but it is
possible to use WaylandEnable=false in /etc/gdm3/custom.conf and reboot.

This refers to Isabelle/5be1b4354638.


I've had this on my TODO list for a long time, desparately waiting for a 
proper arm64-linux version: the problem is actually one of the Gradle build 
tool behind it. Now I've found that the above Wayland window manager problem 
disappears by updating FlatLaf. Apparently we have very few users of standard 
Ubuntu, so it rarely showed up in practice, and was only reported once (where 
I could not reproduce it on the spot).

Normally I would not make such a critical last-minute change just before RC1, 
but the guy behind FlatLaf (Karl Tauber from München-Brunnthal) usually 
delivers very solid releases without regressions.


	Makarius