gpui: Support hitbox blocking mouse interaction except scrolling (#31712)

tl;dr: This adds `.block_mouse_except_scroll()` which should typically
be used instead of `.occlude()` for cases when the mouse shouldn't
interact with elements drawn below an element. The rationale for
treating scroll events differently:

* Mouse move / click / styles / tooltips are for elements the user is
interacting with directly.
* Mouse scroll events are about finding the current outer scroll
container.

Most use of `occlude` should probably be switched to this, but I figured
I'd derisk this change by minimizing behavior changes to just the 3 uses
of `block_mouse_except_scroll`.

GPUI changes:

* Added `InteractiveElement::block_mouse_except_scroll()`, and removes
`stop_mouse_events_except_scroll()`

* Added `Hitbox::should_handle_scroll()` to be used when handling scroll
wheel events.

* `Window::insert_hitbox` now takes `HitboxBehavior` instead of
`occlude: bool`.

    - `false` for that bool is now `HitboxBehavior::Normal`.

    - `true` for that bool is now `HitboxBehavior::BlockMouse`.
    
    - The new mode is `HitboxBehavior::BlockMouseExceptScroll`.

* Removes `Default` impl for `HitboxId` since applications should not
manually create `HitboxId(0)`.

Release Notes:

- N/A

crates/ui/src/components/indent_guides.rs

@@ -136,7 +136,9 @@ pub struct IndentGuideLayout {
 
 /// Implements the necessary functionality for rendering indent guides inside a uniform list.
 mod uniform_list {
-    use gpui::{DispatchPhase, Hitbox, MouseButton, MouseDownEvent, MouseMoveEvent};
+    use gpui::{
+        DispatchPhase, Hitbox, HitboxBehavior, MouseButton, MouseDownEvent, MouseMoveEvent,
+    };
 
     use super::*;
 
@@ -256,7 +258,12 @@ mod uniform_list {
                     .indent_guides
                     .as_ref()
                     .iter()
-                    .map(|guide| window.insert_hitbox(guide.hitbox.unwrap_or(guide.bounds), false))
+                    .map(|guide| {
+                        window.insert_hitbox(
+                            guide.hitbox.unwrap_or(guide.bounds),
+                            HitboxBehavior::Normal,
+                        )
+                    })
                     .collect();
                 Self::PrepaintState::Interactive {
                     hitboxes: Rc::new(hitboxes),

crates/ui/src/components/popover_menu.rs

@@ -2,9 +2,9 @@ use std::{cell::RefCell, rc::Rc};
 
 use gpui::{
     AnyElement, AnyView, App, Bounds, Corner, DismissEvent, DispatchPhase, Element, ElementId,
-    Entity, Focusable as _, GlobalElementId, HitboxId, InteractiveElement, IntoElement, LayoutId,
-    Length, ManagedView, MouseDownEvent, ParentElement, Pixels, Point, Style, Window, anchored,
-    deferred, div, point, prelude::FluentBuilder, px, size,
+    Entity, Focusable as _, GlobalElementId, HitboxBehavior, HitboxId, InteractiveElement,
+    IntoElement, LayoutId, Length, ManagedView, MouseDownEvent, ParentElement, Pixels, Point,
+    Style, Window, anchored, deferred, div, point, prelude::FluentBuilder, px, size,
 };
 
 use crate::prelude::*;
@@ -421,7 +421,7 @@ impl<M: ManagedView> Element for PopoverMenu<M> {
                 ((), element_state)
             });
 
-            window.insert_hitbox(bounds, false).id
+            window.insert_hitbox(bounds, HitboxBehavior::Normal).id
         })
     }
 

crates/ui/src/components/right_click_menu.rs

@@ -2,9 +2,9 @@ use std::{cell::RefCell, rc::Rc};
 
 use gpui::{
     AnyElement, App, Bounds, Corner, DismissEvent, DispatchPhase, Element, ElementId, Entity,
-    Focusable as _, GlobalElementId, Hitbox, InteractiveElement, IntoElement, LayoutId,
-    ManagedView, MouseButton, MouseDownEvent, ParentElement, Pixels, Point, Window, anchored,
-    deferred, div, px,
+    Focusable as _, GlobalElementId, Hitbox, HitboxBehavior, InteractiveElement, IntoElement,
+    LayoutId, ManagedView, MouseButton, MouseDownEvent, ParentElement, Pixels, Point, Window,
+    anchored, deferred, div, px,
 };
 
 pub struct RightClickMenu<M: ManagedView> {
@@ -185,7 +185,7 @@ impl<M: ManagedView> Element for RightClickMenu<M> {
         window: &mut Window,
         cx: &mut App,
     ) -> PrepaintState {
-        let hitbox = window.insert_hitbox(bounds, false);
+        let hitbox = window.insert_hitbox(bounds, HitboxBehavior::Normal);
 
         if let Some(child) = request_layout.child_element.as_mut() {
             child.prepaint(window, cx);

crates/ui/src/components/scrollbar.rs

@@ -3,9 +3,9 @@ use std::{any::Any, cell::Cell, fmt::Debug, ops::Range, rc::Rc, sync::Arc};
 use crate::{IntoElement, prelude::*, px, relative};
 use gpui::{
     Along, App, Axis as ScrollbarAxis, BorderStyle, Bounds, ContentMask, Corners, Edges, Element,
-    ElementId, Entity, EntityId, GlobalElementId, Hitbox, Hsla, IsZero, LayoutId, ListState,
-    MouseDownEvent, MouseMoveEvent, MouseUpEvent, Pixels, Point, ScrollHandle, ScrollWheelEvent,
-    Size, Style, UniformListScrollHandle, Window, quad,
+    ElementId, Entity, EntityId, GlobalElementId, Hitbox, HitboxBehavior, Hsla, IsZero, LayoutId,
+    ListState, MouseDownEvent, MouseMoveEvent, MouseUpEvent, Pixels, Point, ScrollHandle,
+    ScrollWheelEvent, Size, Style, UniformListScrollHandle, Window, quad,
 };
 
 pub struct Scrollbar {
@@ -226,7 +226,7 @@ impl Element for Scrollbar {
         _: &mut App,
     ) -> Self::PrepaintState {
         window.with_content_mask(Some(ContentMask { bounds }), |window| {
-            window.insert_hitbox(bounds, false)
+            window.insert_hitbox(bounds, HitboxBehavior::Normal)
         })
     }