Persist the state of content sidebar while browsing away from viewer and
initializing the same on returning back to the viewer. The state is saved
in persistent store preferences and used upon viewer initialization.
Fixes#6935
We cannot piggy-back on the `updateviewarea` event in order to update the stored sidebar state, since there're a number of cases where opening/switching the sidebar view won't fire a `updateviewarea` event.
Note that `updateviewarea` only fires when the position changes in the *viewer*, which means that it won't fire if e.g. the viewer is narrow, such that the sidebar overlays the document transparently; or when switching views, without the document position also changing.
This patch also moves the handling of `forceOpen` parameter in `PDFSidebar_switchView`, to prevent triggering back-to-back rendering and dispatching of events.
This is a regression from PR 7097.
(Also, out of scope for this PR, but I think that a `setTimeout` value of `1000 ms` is too large. Switching from scrolling to zooming can fell sluggish, and give the impression that nothing happens.)
