meson: add gst-full-version-script option

Can be used to control the exact symbols exported, or not, in libgstreamer-full.

This is useful when building a tailored libgstreamer-full aimed to be run with some specific binaries. By using such version script one can reduce the size of the generated lib by letting the linker garbage collect all the unused APIs.

cc @xclaesse @dabrain34

README.md

@@ -131,6 +131,12 @@ Since *1.20.0* `gst_init_static_plugins()` is called automatically by
 `gst_init()` and applications must not call it manually any more. The header
 file has been removed from public API.
 
+One can use the `gst-full-version-script` option to pass a
+[version script](https://www.gnu.org/software/gnulib/manual/html_node/LD-Version-Scripts.html)
+to the linker. This can be used to control the exact symbols that are exported by
+the gstreamer-full library, allowing the linker to garbage collect unused code
+and so reduce the total library size.
+
 This is an experimental feature, backward uncompatible changes could still be
 made in the future.