Intead of passing around the output of the config generator program,
which consists of paths joined by a separator we can have the generator
simply produce an extra file containing those paths.
This commit only implements the new approach for the core plugins, as
this was needed to avoid spurious meson rebuilds when the pre-commit
hook regenerates the core plugins_cache.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8231>
A JSON configuration file is generated for core plugins, which maps
plugin names with sources to parse for docstrings.
The file is then opened by the configuration generator script, which
will now favor explicitly listed files to (usually wildcarded) paths
passed on its command line.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8231>
