Workspace back and forth (#253)

* implement workspace back and forth

* Make our own ID counter instead of SerialCounter, use a newtype

* Rename FocusWorkspaceBackAndForth to FocusWorkspacePrevious

* Add focus-workspace-previous to tests

* Don't special case in switch_workspace_previous

* Minor clean up

* Add switch_workspace_auto_back_and_forth to tests

* Skip animation on switch_workspace_previous

* Preserve previous_workspace_id on workspace movement

* Make Workspace::id private with a getter

Reduce the chance it gets overwritten.

* Add test for workspace ID uniqueness

* Update previous workspace ID upon moving workspace across monitors

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Co-authored-by: Ivan Molodetskikh <yalterz@gmail.com>

resources/default-config.kdl

@@ -73,6 +73,11 @@ input {
 
     // Focus windows and outputs automatically when moving the mouse into them.
     // focus-follows-mouse
+
+    // Uncomment this to enable workspace auto-back-and-forth.
+    // If enabled, switching to the same workspace by index twice will switch back to the
+    // previous workspace.
+    // workspace-auto-back-and-forth
 }
 
 // You can configure outputs by their name, which you can find
@@ -518,6 +523,9 @@ binds {
     // Alternatively, there are commands to move just a single window:
     // Mod+Ctrl+1 { move-window-to-workspace 1; }
 
+    // Switches focus between the current and the previous workspace.
+    // Mod+Tab { focus-workspace-previous; }
+
     Mod+Comma  { consume-window-into-column; }
     Mod+Period { expel-window-from-column; }