Improve outline panel keyboard navigation (#20385)

Closes https://github.com/zed-industries/zed/issues/20187

Make outline panel more eager to open its entries:

* scroll editor to selected outline entries (before it required an extra
`"outline_panel::Open", { "change_selection": false }` action call)
* make any `Open` action call to behave like `"outline_panel::Open", {
"change_selection": true }` and remove the redundant parameter.
Now opening an entry is equal to double clicking the same entry: the
editor gets scrolled and its selection changes
* add a way to open entries the same way as excerpts are open in multi
buffers (will open the entire file, scroll and place the caret)

* additionally, fix another race issue that caused wrong entry to be
revealed after the selection change

Release Notes:

- Improved outline panel keyboard navigation

assets/keymaps/default-linux.json

@@ -567,9 +567,11 @@
       "ctrl-alt-c": "outline_panel::CopyPath",
       "alt-ctrl-shift-c": "outline_panel::CopyRelativePath",
       "alt-ctrl-r": "outline_panel::RevealInFileManager",
-      "space": ["outline_panel::Open", { "change_selection": false }],
+      "space": "outline_panel::Open",
       "shift-down": "menu::SelectNext",
-      "shift-up": "menu::SelectPrev"
+      "shift-up": "menu::SelectPrev",
+      "alt-enter": "editor::OpenExcerpts",
+      "ctrl-k enter": "editor::OpenExcerptsSplit"
     }
   },
   {