Add mouse wheel handling for ScrollBar/Scrollable

"Works" in both dimensions but:
* Left/write wheel events aren't getting sent by gnome-terminal
* Up/down wheel events are sent REALLY quickly by Ghostty
* Current implementation doesn't do direction inversing

Author: japhb

lib/Terminal/Widgets/ScrollBar.rakumod

@@ -162,7 +162,27 @@ class Terminal::Widgets::HScrollBar
         }
     }
 
-    #| Handle mouse events
+    #| Handle mouse wheel events
+    multi method handle-event(Terminal::Widgets::Events::MouseEvent:D
+                              $event where { .mouse.pressed &&
+                                             .mouse.button  == 6|7 }, AtTarget) {
+        # Take focus even if wheeled over framing instead of content area
+        self.toplevel.focus-on(self);
+
+        # If enabled, process wheel left/right
+        if $.enabled {
+            given $event.mouse.button {
+                when 6 { self.arrow-left-scroll  }
+                when 7 { self.arrow-right-scroll }
+            }
+        }
+        else {
+            # Refresh even not enabled because of focus state change
+            self.full-refresh;
+        }
+    }
+
+    #| Handle mouse click events
     #  XXXX: Handle drag events
     multi method handle-event(Terminal::Widgets::Events::MouseEvent:D
                               $event where !*.mouse.pressed, AtTarget) {
@@ -309,7 +329,27 @@ class Terminal::Widgets::VScrollBar
         }
     }
 
-    #| Handle mouse events
+    #| Handle mouse wheel events
+    multi method handle-event(Terminal::Widgets::Events::MouseEvent:D
+                              $event where { .mouse.pressed &&
+                                             .mouse.button  == 4|5 }, AtTarget) {
+        # Take focus even if wheeled over framing instead of content area
+        self.toplevel.focus-on(self);
+
+        # If enabled, process wheel up/down
+        if $.enabled {
+            given $event.mouse.button {
+                when 4 { self.arrow-up-scroll   }
+                when 5 { self.arrow-down-scroll }
+            }
+        }
+        else {
+            # Refresh even not enabled because of focus state change
+            self.full-refresh;
+        }
+    }
+
+    #| Handle mouse click events
     #  XXXX: Handle drag events
     multi method handle-event(Terminal::Widgets::Events::MouseEvent:D
                               $event where !*.mouse.pressed, AtTarget) {

lib/Terminal/Widgets/Scrollable.rakumod

@@ -1,5 +1,8 @@
 # ABSTRACT: Common role for scrollable widgets
 
+use Terminal::Widgets::Events;
+
+
 #| Common role for scrollable widgets
 role Terminal::Widgets::Scrollable {
     has UInt:D $.x-scroll = 0;
@@ -86,4 +89,22 @@ role Terminal::Widgets::Scrollable {
         self.ensure-x-span-visible($x, $x + (0 max $w - 1));
         self.ensure-y-span-visible($y, $y + (0 max $h - 1));
     }
+
+    #| Handle mouse wheel events
+    multi method handle-event(Terminal::Widgets::Events::MouseEvent:D
+                              $event where { .mouse.pressed &&
+                                             .mouse.button  == 4|5|6|7 }, AtTarget) {
+        # Take focus even if wheeled over framing instead of content area
+        self.toplevel.focus-on(self);
+
+        # Process wheel up/down/left/right
+        given $event.mouse.button {
+            when 4 { self.change-y-scroll: -4 }
+            when 5 { self.change-y-scroll: +4 }
+            when 6 { self.change-x-scroll: -8 }
+            when 7 { self.change-x-scroll: +8 }
+        }
+
+        self.refresh-for-scroll;
+    }
 }