contrib: qt: add install_wrapper.sh

The script is used by enforcing it through the INSTALL_FILE= make
variable and override the copy of .pc files so as to fix the lib=
variable and ensure the .pc file is linked to $(PREFIX)/lib/pkgconfig/
unlike the installed Qt plugins and qml plugins.

contrib/src/qt/install_wrapper.sh

+#!/usr/bin/env sh
+# Copyright (C) 2022 Videolabs
+# This file is distributed under the same license as the vlc package.
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname  "$0" )" && pwd -P)"
+SOURCE="$1"
+DEST="$2"
+
+install -m 644 -p $SOURCE $DEST
+
+# Filter pkg-config files only
+if [ "${SOURCE##*.}" != 'pc' ]; then
+    exit 0
+fi
+
+"${SCRIPT_DIR}/../pkg-static.sh" "${DEST}"
+
+# Filter pkg-config files that are not installed in the main pkg-config folder
+if [ "$(dirname $2)" -ef "${VLC_PREFIX}/lib/pkgconfig" ]; then
+    exit 0
+fi
+
+pkgconfigdir="$(cd "$(dirname "${DEST}")" && pwd -P)"
+
+# Filter packages installed in a pkgconfig/ folder
+if [ "$(basename "${pkgconfigdir}")" -eq "pkgconfig" ]; then
+    exit 0
+fi
+
+sed -i.orig "s,libdir=.*,libdir=${pkgconfigdir}," "${DEST}"
+mkdir -p "${VLC_PREFIX}/lib/pkgconfig"
+ln -sf "${DEST}" "${VLC_PREFIX}/lib/pkgconfig/"