* Harden the new `hideAllViewsExcept()` to not do erroneous things if called when
the binding is already gone.
* Generalize things into `hideAllViewsExcept(thisOne)`:
- Clear `_viewShowing` in there and do the descriptionHeightWorkaround thing
in there too,
- For Photon panels, do all the 'current' attribute setting in there. To show
a panel during transition, I introduced the 'in-transition' attribute.
* I had to make sure not to over-eagerly dispatch 'ViewShowing' events, because
that confuses some,
* Move the temporary panel handling, which contains an ephemeral panelmultiview
instance, internally. This cleans up the hacky, duplicate PanelUI.js code nicely.
* Keep a local copy of `_transitionDetails` to ensure it's still there after transition,
* Harden `_cleanupTransitionPhase()` to only clear the phase that belongs to a
specific transition, _if_ that's passed in as an argument. This resolves any
potential raciness that might occur when `showSubView()` is called again mid-transition.
* Skip the UITour element visibility check when it's inside a panelview, because
too many things need to happen and that check is too simple to be useful in
that case.
MozReview-Commit-ID: 5HpJKs1Ny5j
3f2ca69f96