Blender Git Loki

Fix T90364: buttons (partially) behind animchannel search block search

When channels are scrolled to be (partially) behind the search bar,
their widget buttons would still be interactive, preventing the seach
buttons to be usable.

We have to make sure the events are consumed from the search and dont
reach other UI blocks.
We can do so by flagging the block `UI_BLOCK_CLIP_EVENTS` -- but also
have to make sure the bounds are calculated correctly (otherwise the
check relating `UI_BLOCK_CLIP_EVENTS` in `ui_but_find_mouse_over_ex` wont
trigger properly.

Maniphest Tasks: T90364

Differential Revision: https://developer.blender.org/D12103