Change data structure of keylists. Reducing the balancing overhead and therefore increases performance.
| **Function** | **Master** | **Patch** |
|`draw_summary_channel`| 0.202105s| 0.083874s |
When adding items to the keylist it will store it in a linked list. This linked list is
accompanied with the length (key_len) and a `last_accessed_column`. last_accessed_column is a cursor
that improve the performance when adding new items as they are mostly ordered by frame numbers.
last_accessed_column is reset when a new fcurve/mask/... is added to the keylist.
Before searching or array access. the listbase needs to be converted to an array.
`ED_keylist_prepare_for_direct_access`. After that the caller can use
`ED_keylist_find_*` or `ED_keylist_array*` functions.
The internal array can also be accessed via the `ED_keylist_listbase` function.
The items inside the array link to the previous/next item in the list.
Future optimizations:
* Split the creation of the keylist and drawing to support threaded drawing.
* Use next, prev pointers to find the next element (pose slide/onion skinning).
* Keep the keylists per fcurve separate and being able to join them to group, ob, summary.
* Remove unneeded attributes.
* Find a better solution for keyblocks storage.