This patch implements panel expansion saving and resetting for property
search. While search is active, the panel expansion is based on whether
or not it has a search result. When the search finishes, the panel
expansion returns to its state before the search started. However, any
panels interacted with during the search won't reset their expansion.
This requires adding a new runtime flag for panels to store whether to
use search result status as expansion. It also requires better handling
for animation when panel expansion changes with another new runtime flag.
`UI_panel_is_closed` gets the search-dependent expansion, but it is
intentionally not used to access expansion in every case-- sometimes it's
necessary to use `PNL_CLOSED` directly.
Differential Revision: https://developer.blender.org/D8984
54da72d3cd