fix(popup,undo): show undo-tree visualizer in popup
fix(popup,undo): show undo-tree visualizer in popup

But only if undo-tree-visualizer-diff is disabled. If it's enabled,
undo-tree has its own opinions on how to manage the two windows which
don't mesh well with our popup manager, so we leave undo-tree to its
devices.

Fix: #5617

hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d