typefindhelper: Introduce a new API for working with a GstTypeFind *

typefindhelper: Introduce a new API for working with a GstTypeFind *

Introduce a new API that can return a GstTypeFind * with helper functions
and data set around buffer data.

While at it, drop factory field from GstTypeFindBufHelper. While it was
useful for logging, it was not passed through function arguments and keeping
it for logging would require an additional API increasing the API surface
and making it harder to use.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3296>