media-gfx/gimp: 9999.ebuild update

media-gfx/gimp: 9999.ebuild update

Sync 9999.ebuild with 2.10.14.ebuild and update dependencies.

Live ebuild is now depends on x11-libs/gtk+:3.
The future 2.99.x release will be prepared with GTK+-3.

New USE-flags "javascript", "lua", "python" are added
to add support of this language scripts via gobject-introspection.
This is also repair 9999.ebuild and closes below mentioned bug.

Meson build script is still experimental. No migration to it this time.

Closes: https://bugs.gentoo.org/698730

Signed-off-by: Sergey Torokhov <torokhov-s-a@yandex.ru>
Closes: https://github.com/gentoo/gentoo/pull/13827
Signed-off-by: Joonas Niilola <juippis@gentoo.org>