On some Linux distros, the audio settings dialog was opening with the
wrong size and position. The culprit seems to be the call to setSize()
which was called inside resized(). We now try to avoid calling setSize()
if we would do so inside a resized() call.

Sometimes, changing the bounds of the window inside the DPICHANGED
handler can cause further DPI change events to be processed. Previously,
the scaleFactor set by the "inner" events was also being used when
notifying listeners about the "outer" events, leading to graphical
glitches.

An effect of the bug was that VST2 views in the AudioPluginHost would
occasionally render with an incorrect size and position after dragging
them between displays with different scale factors.

With this change in place, we only notify listeners and update window
bounds once there are no DPI changes in progress.

Previously, plugin views may be set to unexpected sizes by the host,
which could interrupt size updates due to scale factor changes. This
could leave the plugin view at an incorrect size.

To use this feature, derive your AudioProcessor from
VST3ClientExtensions and override getPluginHasMainInput() to return
false. The main input bus will then be designated as an Aux bus, rather
than a Main bus.

This is mainly useful for synth plugins like vocoders, which may need a
sidechain audio input, but which should replace all audio on the channel
with the output of the synth, rather than mixing with the audio input.

The AAX SDK already checks for truncated IDs internally. If any ID is
truncated, details will be written to Pro Tools' log file (you may need
to enable logging first). Search for "AAX_ASSERT" in the log to find
triggered assertions.

This behaves a lot like jassert, but will never emit unused-variable
warnings.

See commit message of a1337a38 for more details

- Add AlertWindow::show() and showAsync() methods that take a MessageBoxOptions argument
  - Add NativeMessageBox::show() and showAsync() methods that take a MessageBoxOptions argument
  - Update the DialogsDemo to demonstrate the new methods
  - Deprecate AlertWindow::showNativeDialogBox() in favour of the NativeMessageBox methods
  - Pass button strings specified in MesssageBoxOptions to native dialog boxes correctly
  - Use modern TaskDialog on Windows for the native dialog box where available