Fix outline items navigation (#22890)

* Follows-up #22224 , by
adjusting `impl PartialEq for OutlineEntryOutline` to compare outline
items' values too.
Before that, all outline items from the same excerpt were considered
equal.

Adds a test for this

* Stops re-revealing items in the outline panel, when it's focused: now,
when someone scrolls over outline panel items, there is no extra work
happening: the "revealed" item is the one scrolled to

Release Notes:

- Fixed outline items not scrolling properly

crates/multi_buffer/src/multi_buffer.rs

@@ -269,7 +269,7 @@ struct ExcerptIdMapping {
 
 /// A range of text from a single [`Buffer`], to be shown as an [`Excerpt`].
 /// These ranges are relative to the buffer itself
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub struct ExcerptRange<T> {
     /// The full range of text to be shown in the excerpt.
     pub context: Range<T>,