Closes #27171

The `outline_panel::Open` action seems to open the outline panel, but
instead, it moves the editor's cursor to the position of the selected
entry in the outline panel. This PR renames it to
`outline_panel::OpenSelectedEntry` for better clarity.

Meanwhile, there is an existing action, `outline_panel::ToggleFocus`,
that should be used for opening the outline panel.

Todo:
- [x] Added migration

Release Notes:

- Renamed `outline_panel::Open` to `outline_panel::OpenSelectedEntry`
for better clarity.