Effects of this change for windows with native titlebars:
- Resizable windows without maximise buttons will now only allow the
  'zoom' behaviour from the rightmost titlebar button (i.e. this button
  will not allow entering full-screen mode)
- Non-resizable windows will grey-out the rightmost titlebar button,
  whether or not the maximise button is enabled

This change allows mouse events (including enter and exit events) to
reach unfocused views on macOS. This matches the behaviour of unfocused
windows on Linux and Windows, where components paint in their "hovered"
states even when the application window is in the background.

As a byproduct of using tracking areas on macOS, we can remove the fake
mouse move generator.

Ideally, we want to pass shortcut keys to the component to handle, and
only fall back to invoking a menu item if the component was unable to
handle the keyboard event, or if the action was triggered by
clicking/selecting an item in the menu itself. The old implementation
tried to work out whether the action was triggered by a shortcut by
checking the event's characters and modifiers. This method was
inaccurate, because some shortcuts (such as arrow keys) may add
unexpected numpad/function modifier flags.

We now try handling shortcut keys directly in the peer, and pass events
up to the superclass (which will forward them to the main menu) if the
event could not be handled.

This commit also adjusts some Objective-C method signatures to use the
correct string encoding for the BOOL type.

Some plugins (Izotope Relay, some older DPF plugins) use NSTrackingAreas
to handle mouse events, but unprocessed events seemingly get passed up
to outer views. Processing these events was causing unexpected
behaviour. For example, if the cursor entered a plugin view while
dragging a JUCE window border, a mouseEnter event was be generated,
interrupting the drag.

We now check whether mouse events were generated by an NSTrackingArea
which does not belong to the JUCE view, and ignore the event in this
case.

This commit also removes the subview from its superview's subview array before re-ordering as the macOS docs don't make any guarantees about what happens when adding a subview that is already contained in the array.

When drawing a popup menu for a target component with a non-unity scale,
the contents of the component were being drawn with an unwanted vertical
offset.

This resolves an issue on macOS Catalina when using
JUCE_COREGRAPHICS_DRAW_ASYNC where windows would sometimes fail to
completely repaint when they were unminimized.

This change will make plugin views (and other heavyweight views) listen
to their containing window, and dismiss any blocking modal components,
such as PopupMenus when the window is moved or resized.

This should fix issues where opening a combobox then moving the plugin
window could leave the combobox's popupmenu 'stranded'.

This behaviour was already present on windows, so this patch updates
Linux and macOS window-handling to match.

This reverts commit a6217ae9fb.