When implementing NDK media support, it would be useful to also have JNI
implementation in the same binary as NDK media compatibility is lower.
As such, implement a rudimentary vtable system for gstamc-codec and
gstamc-format, and allow choosing the implementation at static_init()
time.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4115>
This allows the implementations to do custom logic behind the hood. For
example, when NDK implementation is added, the entrypoint can chooses to
statically initialize the NDK implementations or the JNI one.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4115>
Check that `self` and `self->callback` are defined. `self` can be set to
`NULL` in `remove_listener`, and `self->callback` can be set to `NULL`
inside `gst_amc_surface_texture_jni_set_on_frame_available_callback`.
This can cause a segfault since the Java object can outlive the C
object, and call the callback after `remove_listener` is called.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2024>
