Adapted strategy in GtkMenu to handle any number of enter events

Fixes #1954

Change-Id: I81adacb07d21cd5bc12602cb5dfe9fd0f9d876aa
7 jobs for dropdown_mac_1954 in 25 minutes and 11 seconds
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  Build
passed #1343890
debian-meson

00:11:36

passed #1343887
fedora-autotools

00:14:35

manual #1343888
allowed to fail manual
fedora-distcheck
passed #1343889
fedora-meson

00:07:23

manual #1343892
win32-ps allowed to fail manual
msys2-mingw64-autotools
passed #1343891
win32-ps
msys2-mingw64-meson

00:15:56

 
  Docs
passed #1343893
reference

00:09:14