Add hover_line_number color token (#23279)

This enables having a dedicated color for the line number hover state.
That's relevant because line numbers can now be clicked to jump to
cursor location in multibuffers.

Release Notes:

- N/A

---------

Co-authored-by: João Marcos <marcospb19@hotmail.com>

crates/editor/src/element.rs

@@ -3977,6 +3977,8 @@ impl EditorElement {
 
             let color = if is_active {
                 cx.theme().colors().editor_active_line_number
+            } else if !is_singleton && hitbox.is_hovered(cx) {
+                cx.theme().colors().editor_hover_line_number
             } else {
                 cx.theme().colors().editor_line_number
             };