PR: Handle 'unlocked panes' state for undocking without generating a new window

[dalthviz]

Fixes #5486

[jnsebgosselin]

Thanks for the quick fix @dalthviz. I've tested your solution locally and it is working for all plugins, but it is still crashing with the Editor.

[dalthviz]

Thanks a lot for the testing and feedback @jnsebgosselin 👍

[ccordoba12]

@jnsebgosselin, please approve so I can merge this one :-)

[jnsebgosselin]

I confirm that Spyder is not crashing anymore when dragging plugins with the mouse when Lock panes is unchecked 🎉

Just to be sure everyone understands the implications of these changes before merging, new windows will now be created when undocking plugins only when Lock panes is checked. Spyder will revert to the old behaviour when Lock panes is unchecked, i.e. Spyder will never create new windows when undocking plugins, even when undocking with the buttons.

I think this make sense and I vote 👍 for this change.

[jnsebgosselin]

Some other observations that I'm noting here, but that are maybe out of the scope of this PR:

1. I think that new windows should also be created when undocking plugin from their cog menu when Lock panes is checked. Currently, undocking a plugin from its cog menu never create a new window, whether Lock panes is checked or not.

2. The Undock action in the plugins cog menu is not disabled when undocking plugins through their undock button. This does not generate any bug, so it's not a big deal, but it is confusing a little bit.

3. Instead of disabling the Undock action in the plugin cog menu when it is undocked, I would replaced it by a Dock action.

[ccordoba12]

Some other observations

Thanks Jean for your observations. Please open a new issue about them, so we can discuss them there.