Enable skipping plugins search at build time.

Enable skipping plugins search at build time.

Forwarded: not-needed

This patch sets
QT_SKIP_AUTO_PLUGIN_INCLUSION and QT_SKIP_AUTO_QML_PLUGIN_INCLUSION to ON
by default, thus avoiding unnecesary build dependencies on plugins.

The variables can still be set to OFF by the user at build time, allowing
them to find the packages if necessary. But if you need so for a Debian
package please reach the Qt maintainers first. We want to know why you
need to do so. Thanks in advance!

Gbp-Pq: Name enable_skip_plugins.patch