Blender Git Loki

Anim: Keylist drawing optimization by using arrays.

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.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D12052