multimedia/gpac: merge sub-ports and update to 2.4.0

Consolidate gpac, mp4box and library into a single port as the upstream build
system does not easily support splitting applications from the library.

Sponsored by:	Netflix

Author: ocochard

MOVED

@@ -5079,3 +5079,4 @@ devel/py-confusable_homoglyphs|devel/py-confusable-homoglyphs|2026-01-15|Rename
 devel/py-pyyaml_env_tag|devel/py-pyyaml-env-tag|2026-01-15|Rename to match upstream naming
 www/py-aiohttp_cors|www/py-aiohttp-cors|2026-01-15|Rename to match upstream naming
 lang/cython3|lang/cython|2026-01-15|Remove obsoleted port. Use lang/cython instead
+multimedia/gpac-mp4box|multimedia/gpac|2026-01-15|Merge mp4box and libgpac and add gpac

multimedia/Makefile

@@ -71,8 +71,7 @@
     SUBDIR += get_iplayer
     SUBDIR += gmmlib
     SUBDIR += gmp-api
-    SUBDIR += gpac-libgpac
-    SUBDIR += gpac-mp4box
+    SUBDIR += gpac
     SUBDIR += gpodder
     SUBDIR += gst123
     SUBDIR += gstreamer1