Use a double instead of a plain float for intermediary
property values, so we have enough bits to store INT_MAX
and it doesn't get rounded and wrapped to -1 when cast
back to a 32-bit integer.
Fixes criticals like
g_param_spec_int: assertion 'default_value >= minimum && default_value <= maximum' failed
when loading LADSPA plugins from the Linux Studio Plugins
Project (http://lsp-plug.in) in GStreamer.
Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/issues/1194
Split the introspection and registration part. This way we only need to open all
plugins when updating the registry. When reading the registry we can register
the elements entierly from the cache.
