it seems the descriptors can't be seen anyway on welcome screen

to be able to test if pattern is applyable without obtaining a `PsiClass`

Now uninitialized field value is a memory state precondition instead of directly pushed value

When tabs with the same prefix are merged, contentManager.findContent can only find content for the tab currently shown, not the other ones.
To properly find and close content by name in this case, need to examine corresponding TabbedContext and find a component inside it.

EA-106444

It was used in tests, but not needed any longer.

it seems the descriptors can't be seen anyway on welcome screen

"Preparing for rebase" can be used only before the interactive rebase dialog is shown,
afterwards it should be substituted with "Rebasing". However, it is a bit tedious to customize the progress text at that stage, so keeping it simple for now.

IDEA-178172 Good code is yellow: Inspection "@NotNull/@Nullable problems": @NotNull field with non-trivial setter