Add desktop support for going back from the steps

[ai]

We have <TwoStepPage> and the logic to move back in those steps for mobile.

We need to add the same back logic to desktop cases:

1. We need to add some header to second step with × button. We should not show this header on mobile.
2. We should check that Escape works as expected and also closes second step. We need to be sure, that it doesn’t have conflict with keyux jumps.
   1. We need to test all 3 cases: Slow posts, Feed add, Feed categories
   2. We need to test Esc after keyboard interactions (hotkeys, arrows, Enter) and after the mouse clicks

[ilyatitovich]

I want to take it