fix(pane/#3538): Focus pane on mouse click (#3541)

Fixes #3538

Author: bryphe

CHANGES_CURRENT.md

@@ -85,6 +85,7 @@
 - #3532 - OSX: Fix crash when opening folder with Unicode characters (fixes #3519)
 - #3533 - Completion: Fix hang when detail text is large
 - #3537 - Terminal: Fix pasted text showing in reverse order (fixes #3513)
+- #3541 - Pane: Shoudl grab focus when clicked (fixes #3538)
 
 ### Performance
 

src/Feature/Pane/Feature_Pane.re

@@ -18,6 +18,7 @@ type command =
 
 [@deriving show({with_path: false})]
 type msg('inner) =
+  | PaneClicked
   | TabClicked({index: int})
   | CloseButtonClicked
   | ToggleMaximizeButtonClicked
@@ -144,6 +145,8 @@ let update = (msg, model) =>
       Nothing,
     )
 
+  | PaneClicked => (model, GrabFocus)
+
   | TabClicked({index}) => ({...model, selected: index}, Nothing)
 
   | Toggle({paneId}) => toggle(~paneId, model)
@@ -462,7 +465,8 @@ module View = {
             ~isFocused,
             ~theme,
             ~height,
-          )}>
+          )}
+          onMouseUp={_ => dispatch(PaneClicked)}>
           <View style=Styles.resizer>
             <ResizeHandle.Horizontal
               onDrag={delta =>