editor: Do not insert scrollbar hitboxes when scrollbars are never to be shown (#29316)

Finn Evers created 

This PR fixes an issue where scrollbar hitboxes were still inserted for
editors despite scrollbars being programmatically disabled via the
`show_scrollbars`field. This is basically the same fix as in #27467.

The thought process here is that the motivation for `show_scrollbars` is
not to just hide the scrollbars in the editor, but to fully disable
scrollbars for the associated editor. However, this is currently not the
case, as a functioning hitbox for each scrollbar is stil inserted. For
example, the behavior with the old assistant panel can be seen below:


https://github.com/user-attachments/assets/18af6338-dd28-4794-a6a6-5b9691b243f2

Whilst the scrollbar is not visible, there is still a scrollbar hitbox
inserted which triggers hover events and is fully functioning.


This PR fixes this by fully skipping the scrollbar layouting whenever
`show_scrollbars` is set to false, preventing the hitboxes from being
inserted.


https://github.com/user-attachments/assets/b6bb6dc7-902f-4383-bf03-506d0a57ec77


Release Notes:

- N/A

Change summary

crates/editor/src/element.rs | 61 ++++++++++++++++++-------------------
1 file changed, 30 insertions(+), 31 deletions(-)

Detailed changes

crates/editor/src/element.rs 🔗 

@@ -1449,7 +1449,7 @@ impl EditorElement {
         window: &mut Window,
         cx: &mut App,
     ) -> Option<EditorScrollbars> {
-        if !snapshot.mode.is_full() {
+        if !snapshot.mode.is_full() || !self.editor.read(cx).show_scrollbars {
             return None;
         }
 
@@ -1462,36 +1462,35 @@ impl EditorElement {
         }
 
         let scrollbar_settings = EditorSettings::get_global(cx).scrollbar;
-        let show_scrollbars = self.editor.read(cx).show_scrollbars
-            && match scrollbar_settings.show {
-                ShowScrollbar::Auto => {
-                    let editor = self.editor.read(cx);
-                    let is_singleton = editor.is_singleton(cx);
-                    // Git
-                    (is_singleton && scrollbar_settings.git_diff && snapshot.buffer_snapshot.has_diff_hunks())
-                    ||
-                    // Buffer Search Results
-                    (is_singleton && scrollbar_settings.search_results && editor.has_background_highlights::<BufferSearchHighlights>())
-                    ||
-                    // Selected Text Occurrences
-                    (is_singleton && scrollbar_settings.selected_text && editor.has_background_highlights::<SelectedTextHighlight>())
-                    ||
-                    // Selected Symbol Occurrences
-                    (is_singleton && scrollbar_settings.selected_symbol && (editor.has_background_highlights::<DocumentHighlightRead>() || editor.has_background_highlights::<DocumentHighlightWrite>()))
-                    ||
-                    // Diagnostics
-                    (is_singleton && scrollbar_settings.diagnostics != ScrollbarDiagnostics::None && snapshot.buffer_snapshot.has_diagnostics())
-                    ||
-                    // Cursors out of sight
-                    non_visible_cursors
-                    ||
-                    // Scrollmanager
-                    editor.scroll_manager.scrollbars_visible()
-                }
-                ShowScrollbar::System => self.editor.read(cx).scroll_manager.scrollbars_visible(),
-                ShowScrollbar::Always => true,
-                ShowScrollbar::Never => return None,
-            };
+        let show_scrollbars = match scrollbar_settings.show {
+            ShowScrollbar::Auto => {
+                let editor = self.editor.read(cx);
+                let is_singleton = editor.is_singleton(cx);
+                // Git
+                (is_singleton && scrollbar_settings.git_diff && snapshot.buffer_snapshot.has_diff_hunks())
+                ||
+                // Buffer Search Results
+                (is_singleton && scrollbar_settings.search_results && editor.has_background_highlights::<BufferSearchHighlights>())
+                ||
+                // Selected Text Occurrences
+                (is_singleton && scrollbar_settings.selected_text && editor.has_background_highlights::<SelectedTextHighlight>())
+                ||
+                // Selected Symbol Occurrences
+                (is_singleton && scrollbar_settings.selected_symbol && (editor.has_background_highlights::<DocumentHighlightRead>() || editor.has_background_highlights::<DocumentHighlightWrite>()))
+                ||
+                // Diagnostics
+                (is_singleton && scrollbar_settings.diagnostics != ScrollbarDiagnostics::None && snapshot.buffer_snapshot.has_diagnostics())
+                ||
+                // Cursors out of sight
+                non_visible_cursors
+                ||
+                // Scrollmanager
+                editor.scroll_manager.scrollbars_visible()
+            }
+            ShowScrollbar::System => self.editor.read(cx).scroll_manager.scrollbars_visible(),
+            ShowScrollbar::Always => true,
+            ShowScrollbar::Never => return None,
+        };
 
         Some(EditorScrollbars::from_scrollbar_axes(
             scrollbar_settings.axes,