Initial AssetList API & use it to load assets for the asset view tempate

Lots of hacks and temporary code here. I wanted a first working version to find
possible pain points before getting into details.

Basic idea is to store each asset library in an `AssetList`, with a globally
accessible storage. Internally the list uses the File Browser's `FileList`
which already does a fair amount of heavy lifting (threaded file & external
asset reading, lazy loading of visible previews, ...). The File Browser could
access the global asset-list storage as well.

The asset view template uses the new asset list to load and display the assets.

Current state: {F9856940}

Open TODOs: https://developer.blender.org/maniphest/query/M6RWFxFSDor3/#R

1 files changed, 17 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/versioning_290.c b/source/blender/blenloader/intern/versioning_290.c
index 29041f4ae9d..fedc003e4ff 100644
--- a/source/blender/blenloader/intern/versioning_290.c
+++ b/source/blender/blenloader/intern/versioning_290.c
@@ -1755,4 +1755,21 @@ void blo_do_versions_290(FileData *fd, Library *UNUSED(lib), Main *bmain)
 
     /* Keep this block, even when empty. */
   }
+
+  {
+    if (!DNA_struct_elem_find(
+            fd->filesdna, "View3D", "AssetLibraryReference", "active_asset_library")) {
+      LISTBASE_FOREACH (bScreen *, screen, &bmain->screens) {
+        LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+          LISTBASE_FOREACH (SpaceLink *, space, &area->spacedata) {
+            if (space->spacetype == SPACE_VIEW3D) {
+              View3D *v3d = (View3D *)space;
+              v3d->active_asset_library.type = ASSET_LIBRARY_LOCAL;
+              v3d->active_asset_library.custom_library_index = -1;
+            }
+          }
+        }
+      }
+    }
+  }
 }