Add option to build as static Qt imageformats plugins
This patch adds an option to allow build static Qt plugins which can be used with developer's own Qt builds or existing static Qt distributions like MSYS2's qt5-static
/qt6-static
package.
This patch didn't install any extra configuration files so developers still need to link to these libraries manually, and use Q_IMPORT_PLUGIN(XXXPlugin)
to register the plugin.
Related: #4 (closed) (please see this issue for more related discussion)