Fix mutter 3.3x crashes

[Tireg]

This PR fixes issues against running upstream gala with mutter 3.3x.
This should fix #634

Every single patch is detailed in this post: #634 (comment)
I reported every step as a commit comment in order to understand it more easily.

[tintou]

By creating an unowned List you're creating a leak here

[Tireg]

By creating an unowned List you're creating a leak here

For each one of the suggestions, we fill the list using manager.get_workspace_by_index (i). I don't know Vala but isn't there something like List<unowned Workspace> (instead of List<Workspace>) that I should use in order to avoid destroying the Workspaces objects when the List is destroyed ?

Just to be sure there is no mistake.

Edit:

Ok I just tested it, it seems to work without unowned so I added the changes.
Not quite sure to understand why unowned is not needed however.

I just noticed I should have accepted the changes directly from github instead of pushing a new commit however.

[tintou]

@Tireg a new commit is fine too, no worries :)
The difference here:
List<unowned Workspace> means that we have to free the List but not the elements
List<Workspace> means that we have to free the list and unref the elements
Defined as List<Workspace>, Vala will take care to increase the reference count before adding an element to the list, when List<unowned Workspace> would not ref the workspace, so List<Workspace> is safer for us in this case.

[decathorpe]

I'm looking forward to testing this on fedora :)

Just one question / nit-pick: The name for the gsettings override file seems rather odd:

20_elementary.pantheon.wm.gschema.override

Can we rename it to something like 20_io.elementary.gala.gschema.override instead?

[tintou]

@decathorpe Yeah, would make sense too :)

[decathorpe]

Hm. I'm still getting a reproducible crash on startup on fedora 31 :( I'll try to file a new bug report for it, once I'm able to provide a useful traceback :(