editor: Add trailing whitespace rendering (#32329)

Closes #5237

- Adds "trailing" option for "show_whitespaces" in settings.json
- Supports importing this setting from vscode

The option in question will render only whitespace characters that
appear after every non-whitespace character in a given line.

Release Notes:

- Added trailing whitespace rendering

crates/editor/src/element.rs

@@ -7329,6 +7329,17 @@ impl LineWithInvisibles {
                 paint(window, cx);
             }),
 
+            ShowWhitespaceSetting::Trailing => {
+                let mut previous_start = self.len;
+                for ([start, end], paint) in invisible_iter.rev() {
+                    if previous_start != end {
+                        break;
+                    }
+                    previous_start = start;
+                    paint(window, cx);
+                }
+            }
+
             // For a whitespace to be on a boundary, any of the following conditions need to be met:
             // - It is a tab
             // - It is adjacent to an edge (start or end)