fix: data trees go with the systems they serve

Choosing GBA alone brought FBNeo's cheats and samples, 3,472 files,
because both trees listed every FBNeo system. The profile now names the
systems each serves, from the code: a driver's <name>.ini, cheat.dat,
cheatnes.dat or cheatsnes.dat (conc.cpp:815-828, 1059-1083), the md_,
pce_, tg_ and sgx_ drivers the tree holds, and samples read by arcade
drivers alone (samples.cpp:886-899).

The list now gives a tree the platform's ids its systems normalize to,
as a core extra's: the cheats said sega-megadrive where RetroArch says
sega-mega-drive, and a tree no platform system serves goes with the
files of none, as the pack puts it. The installer keeps a tree for the
systems chosen by name, not for every system a shared file names: the
arcade choice took blueMSX's machines through msx.zip.

scripts/generate_pack.py

@@ -78,6 +78,7 @@ from common import (
     load_platform_config,
     without_profile_blind,
     MANUFACTURER_PREFIXES,
+    _norm_system_id,
     require_yaml,
     ProfileSelectionError,
     core_system_dirs,
@@ -5113,7 +5114,7 @@ def generate_manifest(
     data_sizes = pack_only_sizes + [os.path.getsize(src) for src, _dest in data_members]
     data_directories = _manifest_data_directories(
         data_members, data_refs, data_registry or {}, base_dest,
-        tree_readers(pack_systems, core_trees),
+        tree_readers(pack_systems, core_trees), pack_systems,
     )
 
     now = _build_timestamp(db)
@@ -5219,6 +5220,7 @@ def _manifest_data_directories(
     registry: dict,
     base_dest: str,
     readers: dict[str, list[str]] | None = None,
+    platform_systems: Iterable[str] | None = None,
 ) -> list[dict]:
     """Each data directory the pack carries, as the installer rebuilds it.
 
@@ -5229,6 +5231,11 @@ def _manifest_data_directories(
     changed since is refused rather than installed. archive_size is the
     size of the archive refresh_data_dirs last downloaded, what fetching
     the tree costs: a tarball whose tree is 10 KB is a download of 21 MB.
+    ``systems`` are the platform's ids (``platform_systems``) the tree's
+    systems normalize to, as a core extra's are: a tree no platform system
+    serves has none, and goes with the files of no system, as the pack
+    built with --system puts it in the part of its own. FBNeo's cheats
+    carried sega-megadrive where RetroArch's list says sega-mega-drive.
     ``optional`` marks a tree every core reading it runs without
     (``required: false``): install.py --required-only leaves it out, as the
     pack built with --required-only does. ``cores`` names the cores that
@@ -5237,8 +5244,13 @@ def _manifest_data_directories(
     """
     grouped: dict[tuple[str, str], dict] = {}
     versions: dict[str, dict[str, dict]] = {}
+    by_norm: dict[str, list[str]] = {}
+    for sys_id in sorted(platform_systems or ()):
+        by_norm.setdefault(_norm_system_id(sys_id), []).append(sys_id)
     for src, full in members:
         ref, systems, prefix, needed = refs[full]
+        if platform_systems is not None:
+            systems = tuple(own for sid in systems for own in by_norm.get(_norm_system_id(sid), ()))
         entry = registry.get(ref, {})
         key = (ref, prefix)
         group = grouped.get(key)