- This allows users to show plugins directly undocked, i.e. without
making them first visible but docked on the main window to then undock
them.
- Also, improve typing a bit.

- To close it the user can click the Close action in its Options menu or
go to the Panes menu.
- Hide the Outline's Undock and Lock/unlock actions when shown in the
maximized editor because it doesn't make sense to show them in that
case.

…g system

That allows to make persistent that state across Spyder sessions.

That will allow us to use it in other tests.

- Also, check the visibility of the Outline when shown with the
maximized editor.
- Fix test_no_update_outline because it was failing.

- Reduce their size to make them a bit smaller than the QMainWindow
separators. That will help users to navigate our UI more easily.
- Also, remove images of QMainWindow separators because they are not
visible.

This will present to users the same UI as the one shown when the editor
is maximized.

This will allow us to reuse those menus in other places they are needed.

- This will allow us to easily access them in other places.
- Also, fix typing and improve code style in its container.

That way it'll be easier to create those kind of toolbars in other
widgets.

This provides a very similar UX to the one users see when maximizing the
editor in the main window.

- This preserves the checked state of new Outline action shown in the
View menu.
- It also removes the handle which looks like an extra and odd border in
the window.

- That way it can be used by other plugins or widgets.
- Use it to set the menubar stylesheet of EditorMainWindow.

- Also, fix failing tests for the Working directory.

Also, check for the presence of splitter handler because it can't be
available during tests.

This was causing a crash at startup in some cases.

- Also, remove unnecessary condition in test_undock_plugin_and_close and
style from the app stylesheet.

Co-authored-by: Jitse Niesen <jitseniesen@yahoo.com>

This helps to have a more straightforward UI because "Move" means
basically "Move to another position". And "Lock" means "Lock position".

Also, remove a couple of unneeded imports.

- We were not unmaximizing a possibly maximized plugin before the
switch, which left the window in an inconsistent state.
- We also need to reapply the dock tabbar style after the switch so the
window looks as expected.