We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
With two exceptions:
* ges_clip_create_track_elements_func
* ges_uri_clip_set_uri
which were never declared in headers and should always have been static.
+ Generate the documentation
Note: Do not compile (add to Makefile.am) for now as we are missing pieces at that point
Co-Authored-By: Volodymyr Rudyi <vladimir.rudoy@gmail.com>