Fix #145711: Packed images may fail to export with USD

Certain packed images, like those loaded directly into memory with
`BKE_image_packfiles_from_mem`, would cause USD to process the images as
"in memory" rather than as "packed" because the API was not removing the
IMG_GEN_TILE flag.

Additionally, be sure to use the packed filepath whenever possible
rather than the name given to the Image datablock as this ensures the
correct file names are used inside the USD file and for the resulting
file on disk after export.

This also fixes 2 render tests which now match when compared to the
native renders.

Pull Request: https://projects.blender.org/blender/blender/pulls/145749

source/blender/blenkernel/intern/image.cc

@@ -1527,6 +1527,10 @@ void BKE_image_packfiles_from_mem(ReportList *reports,
     imapf->view = 0;
     imapf->tile_number = 1001;
     STRNCPY(imapf->filepath, ima->filepath);
+
+    /* The image should not be marked as "generated" since image data was provided. */
+    ImageTile *base_tile = BKE_image_get_tile(ima, 0);
+    base_tile->gen_flag &= ~IMA_GEN_TILE;
   }
 }
 

source/blender/io/usd/intern/usd_writer_material.cc

@@ -784,6 +784,14 @@ static std::string get_in_memory_texture_filename(Image *ima)
   BKE_image_release_ibuf(ima, imbuf, nullptr);
 
   char file_name[FILE_MAX];
+
+  /* NOTE: Any changes in packed filepath handling here should be considered alongside potential
+   * changes in `export_packed_texture`. The file name returned needs to match. */
+  if (is_packed && ima->filepath[0] != '\0') {
+    BLI_path_split_file_part(ima->filepath, file_name, FILE_MAX);
+    return file_name;
+  }
+
   /* Use the image name for the file name. */
   STRNCPY(file_name, ima->id.name + 2);