[IJPL-43620] [platform] Custom Ordering for Status Bar Items

[jakub-bochenski]

At first I tried implementing user ordering using LoadingOrder:

• currently the order of widgets in status bar is defined by plugins, using anchors like after LineSeparator
• we want to allow the user to override this order
• naive approach fails because, you might have two widgets A and B, typically B is after A but the user rearranges them, it will cause an exception if another widget has anchor like after A, before B
• trying to override all the anchors and "linearize" them (sequential after anchors as per desired visual order), only helps assuming no new widgets are added,
  • even considering all currently available widgets (active and inactive) this will still fail if a new plugin that contributes status bar widgets is installed later
• since widgets can be added and removed, there is a need for an algorithm to reconcile the order desired by the user and the default order defined by the plugins
• there is no obvious, simple approach; this is a partial-order merge problem, this would require extending the DFSTBuilder.java class to support weighted edges

So I implemented a different approach.
User moves are recorded separately and applied after the LoadingOrder sorting is applied (WidgetSorter)

I didn't find any tests covering the status bar.
I've added a unit test to verify that the widgets are sorted correctly.

I've also fixed com.intellij.openapi.wm.impl.status.IdeStatusBarImplKt#wrap method to set WIDGET_IT.
Missing WIDGET_IT was preventing DnD from working.