- A repaint will always occur from a lookAndFeelChanged

- Created a new detail namespace
- Moved shared module implementation details into the detail namespace
- Split dependencies so source files only rely on details in the detail namespace
- Removed all code from the juce_gui_basics.cpp file

The biggest new feature in this commit is the addition of
NativeMessageBox::scopedAsync and AlertWindow::scopedAsync, both of
which return an instance of ScopedMessageBox that will hide the message
box in its destructor.

The code for displaying modal dialogs on Windows has also been updated.
Now, the dialog itself is run from a new thread with its own message
loop. This means that when the dialog is dismissed, the background
thread can be joined safely. In plugins, this means that there's no
danger of the plugin view being destroyed from within the message box
runloop, for example.

This is a breaking change - see BREAKING-CHANGES.txt

This change avoids a situation where a standalone plugin's Audio/Midi
settings window could appear in a wrong position.

Previously, individual components had to ask the peer to hide and show
the keyboard, by calling textInputRequired() and
dismissPendingTextInput() respectively. When an onscreen keyboard (OSK)
was required, most Peer implementation would directly hide/show the OSK
inside these function. However, the iOS ComponentPeer implementation
instead listened to the application's global keyboard focus, and only
opened the OSK when the focused component was also a TextInputTarget
with active input.

The iOS scheme seems like a better design, as it enforces that the OSK
hiding and showing is synced with the keyboard focus of the application.
In the other implementations, it was possible for a Component to call
textInputRequired even when it didn't have the keyboard focus, putting
the application into an inconsistent state. The iOS scheme also makes
the TextInputTarget interface more useful, as it enforces that the OSK
will only display for components that implement TextInputTarget, and
return true from isTextInputActive().

This patch changes all Peer implementations to match the iOS
implementation, improving consistency. Each time the global keyboard
focus changes, refreshTextInputTarget is called automatically, and the
OSK is shown if the focused component is a TextInputTarget that returns
true from isTextInputActive, and hidden otherwise. Components can also
call refreshTextInputTarget manually. This should be done whenever the
component updates the return value of isTextInputActive(). Effectively,
the Peer is now responsible for keeping track of the focused
TextInputTarget, rather than allowing individual components to hide and
show the OSK at will.

Additionally, this patch adds an option to the TextEditor to
automatically dismiss the OSK when the mouse is clicked outside of the
editor. This should improve user experience on mobile platforms, where
touches on sibling components may cause a TextEditor to gain keyboard
focus and unnecessarily display the OSK.

Previously, individual components had to ask the peer to hide and show
the keyboard, by calling textInputRequired() and
dismissPendingTextInput() respectively. When an onscreen keyboard (OSK)
was required, most Peer implementation would directly hide/show the OSK
inside these function. However, the iOS ComponentPeer implementation
instead listened to the application's global keyboard focus, and only
opened the OSK when the focused component was also a TextInputTarget
with active input.

The iOS scheme seems like a better design, as it enforces that the OSK
hiding and showing is synced with the keyboard focus of the application.
In the other implementations, it was possible for a Component to call
textInputRequired even when it didn't have the keyboard focus, putting
the application into an inconsistent state. The iOS scheme also makes
the TextInputTarget interface more useful, as it enforces that the OSK
will only display for components that implement TextInputTarget, and
return true from isTextInputActive().

This patch changes all Peer implementations to match the iOS
implementation, improving consistency. Each time the global keyboard
focus changes, refreshTextInputTarget is called automatically, and the
OSK is shown if the focused component is a TextInputTarget that returns
true from isTextInputActive, and hidden otherwise. Components can also
call refreshTextInputTarget manually. This should be done whenever the
component updates the return value of isTextInputActive(). Effectively,
the Peer is now responsible for keeping track of the focused
TextInputTarget, rather than allowing individual components to hide and
show the OSK at will.

Additionally, this patch adds an option to the TextEditor to
automatically dismiss the OSK when the mouse is clicked outside of the
editor. This should improve user experience on mobile platforms, where
touches on sibling components may cause a TextEditor to gain keyboard
focus and unnecessarily display the OSK.

The helper function setComponentAsyncLayerBackedViewDisabled has been replaced
by a windowRequiresSynchronousCoreGraphicsRendering ComponentPeer style flag.

This partially reverts f43784dc: "macOS:  Propagate focus loss message when resigning key window status and only grab focus if window can become the key window"

Showing the tip will in turn call getDesktopScaleFactor(), accessing the
lastComponentUnderMouse. In some cases, it was possible for
lastComponentUnderMouse to point to a deleted component, resulting in
UB.

There are two changes in this PR:
- Using a SafePointer rather than a raw pointer ensures that calls to
  getDesktopScaleFactor() will always be safe, regardless of when they
  happen.
- Moving the assignment of lastComponentUnderMouse to before the call to
  displayTipInternal() ensures that the returned scale factor is that of
  the component that the mouse is currently hovering.