appimage: Fix/set some features for Qt

• Replace not existing FEATURE_qt_freetype=ON with

FEATURE_system_freetype=ON; we want Qt to use the freetype that we build

• Replace not existing FEATURE_system_pcre=ON with

FEATURE_system_pcre2=ON

• Replace not existing FEATURE_system_zstd=ON with

FEATURE_system_zlib=ON; zstd instead of zlib was likely a typo because
Qt doesn't include a copy of zstd

• None of the above changes change the build; they just make explicit

what was already used implicitly

• Add FEATURE_wayland_server=OFF; only the wayland client library is

needed

• GnuPG-bug-id: T7509