This fixes an X11 scrolling issue where Zed may jump by a large amount
due to the scroll valuator state not being reset when the window loses
focus. If you Alt-Tab away from Zed, scroll in another application, then
return, the first scroll event in Zed applies the entire accumulated
delta instead of a single step.

The missing FocusOut reset was originally identified in issue #34901.

Resetting scroll positions on FocusOut matches the behavior already
implemented in the XinputLeave handler and prevents this jump.

Closes #34901
Closes #40538

Release Notes:

- Fixed an X11 issue where Alt-Tabbing to another application,
scrolling, and returning to Zed could cause the next scroll event to
jump by a large amount.