appimage build: bundle dependencies of Qt xcb plugin

fixes #7198

We recently bumped the bundled version of PyQt (5.14.2->5.15.4).
It seems the new version has a lot more dynamic dependencies.

From https://doc.qt.io/qt-5/linux-requirements.html :
> From Qt 5.15 onwards, Qt does require libxcb 1.11. Also, the -qt-xcb
> configure option got removed that was bundling some of the libs below.

We are using the prebuilt wheels for PyQt5 from PyPI. Presumably those
had previously been built using the -qt-xcb option.

contrib/build-linux/appimage/Dockerfile

@@ -28,8 +28,21 @@ RUN apt-get update -q && \
         libzbar0=0.10+doc-10ubuntu1  \
         libdbus-1-3=1.10.6-1ubuntu3.6 \
         libxkbcommon-x11-0=0.5.0-1ubuntu2.1 \
-        libxcb-util1=0.4.0-0ubuntu3 \
+        libxcb1=1.11.1-1ubuntu1 \
         libxcb-xinerama0=1.11.1-1ubuntu1 \
+        libxcb-randr0=1.11.1-1ubuntu1 \
+        libxcb-render0=1.11.1-1ubuntu1 \
+        libxcb-shm0=1.11.1-1ubuntu1 \
+        libxcb-shape0=1.11.1-1ubuntu1 \
+        libxcb-sync1=1.11.1-1ubuntu1 \
+        libxcb-xfixes0=1.11.1-1ubuntu1 \
+        libxcb-xkb1=1.11.1-1ubuntu1 \
+        libxcb-icccm4=0.4.1-1ubuntu1 \
+        libxcb-image0=0.4.0-1build1 \
+        libxcb-keysyms1=0.4.0-1 \
+        libxcb-util1=0.4.0-0ubuntu3 \
+        libxcb-render-util0=0.3.9-1 \
+        libx11-xcb1=2:1.6.3-1ubuntu2.2 \
         libc6-dev=2.23-0ubuntu11.2 \
         && \
     rm -rf /var/lib/apt/lists/* && \