Fix a problem where second and later tabs in a window with a left-side tab bar that's limited by the 1/3 * content size bound will have fewer columns than it should. Issue 6371.

Fix a bug where when the left-side tab bar or the toolbelt got resized smaller, only the current tab's splitview's width was adjusted. When that tab was closed, the other splitviews were larger and the window's size was based on them in fitWindowToTabs. This commit changes such drag operations to call fitTabsToWindow when dragging completes so all the splitviews will have the size size. See issue 4323.

Add a control to appearance prefs for whether to show tabs in fullscreen. Make the setting affect all windows rather than having a per-window setting.

Try to fix a crash where the iTermTabBarControlView's delegate is a dangling pointer because PseudoTerminal got released before iTermTabBarControlView. Not sure if this will work but it is cleaner, at least.