Crates using gst_plugin_define might not (need to) import `glib`
directly into their scope; use the one imported in `gstreamer`s root
to make this macro more portable.
Besides, `glib` is prefixed with `$crate::` just below.
They can actually be shared with multiple threads at the same time
safely as all functions requiring an immutable reference are
thread-safe.
OTOH TypeFind can't be shared safely between different threads as not
all implementations of the TypeFind struct are thread-safe.
With rustc 1.40.0, clippy checks that the `unsafe` functions come with
a `Safety` section. When running clippy on a downstream crate, the
macros such as `gst_plugin_define!` leak the clippy warnings for the
unsafe functions.
Silence the warnings for now.
