Add support for resizing panes using vim motions (#21038)

Closes #8628

Release Notes:

- Added support for resizing the current pane using vim keybinds with
the intention to follow the functionality of vim
  - "ctrl-w +" to make a pane taller 
  - "ctrl-w -" to make the pane shorter
  - "ctrl-w >" to make a pane wider
  - "ctrl-w <" to make the pane narrower
- Changed vim pre_count and post_count to globals to allow for other
crates to use the vim count. In this case, it allows for resizing by
more than one unit. For example, "10 ctrl-w -" will decrease the height
of the pane 10 times more than "ctrl-w -"
- This pr does **not** add keybinds for making all panes in an axis
equal size and does **not** add support for resizing docks. This is
mentioned because these could be implied by the original issue

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/workspace/src/workspace.rs

@@ -2988,6 +2988,12 @@ impl Workspace {
         }
     }
 
+    pub fn resize_pane(&mut self, axis: gpui::Axis, amount: Pixels, cx: &mut ViewContext<Self>) {
+        self.center
+            .resize(&self.active_pane.clone(), axis, amount, &self.bounds);
+        cx.notify();
+    }
+
     fn handle_pane_focused(&mut self, pane: View<Pane>, cx: &mut ViewContext<Self>) {
         // This is explicitly hoisted out of the following check for pane identity as
         // terminal panel panes are not registered as a center panes.