treeview: Don't invalidate whole tree unless needed

treeview: Don't invalidate whole tree unless needed

We currently invalidate the whole tree every time the style state
changes in the tree view. The primary reason for this is to catch
default font changes as that may affect text cell renderers. But
cell renderers could *potentially* also read other style properties
(although that seems weird and unlikely).

We handle this by invalidating only when some state that affects sizes
is changed. This includes all the font properties.