a559fb833c
Add support to select multiple tree view elements (similar to outliner/anim channels) `Ctrl + LMB` to select+activate element under the mouse `Shift + LMB` to select all items between active and clicked item. As of now, only Shape key has support for multi-select. (straightforward to include other views). `KEYBLOCK_SEL` flag is used for storing selection state. Pull Request: https://projects.blender.org/blender/blender/pulls/138979