VST3 Client: Make window sizing slightly more robust in Live

The following was observed for a VST3 plugin hosted in Live 11.1 with
auto-scaling disabled:

- It never calls setContentScaleFactor on the plugin's UI, so the
  wrapper has to check the current display on a timer and update the
  current scale factor when necessary.

- It calls canResize on the plugin view after opening it, but doesn't
  seem to respect the result of this call. According to the VST3
  documentation, a host is supposed to only call checkSizeConstraint
  during a live resize operation (which should only happen if the plugin
  reports it can resize), but Live calls this function every time the
  user drags the editor. It also passes the result of this function to
  onSize, whether or not checkSizeConstraints reported success.

- When dragging an editor between displays, Live will continue to call
  checkSizeConstraint and onSize with the editor’s old size in physical
  pixels. In some cases, JUCE's "scale factor check" timer callback
  fires, resizes the view to the correct size, and then Live
  asynchronously calls onSize again with the editor's old size in
  physical pixels, resulting in the editor being set to the wrong
  logical size.

This patch ensures that checkSizeConstraint always returns the current
size of a nonResizable editor. This means that the logical size of the
editor should not change when the result of checkSizeContraint is used
to resize the window.

modules/juce_audio_plugin_client/VST3/juce_VST3_Wrapper.cpp

@@ -1780,7 +1780,20 @@ private:
             {
                 if (auto* editor = component->pluginEditor.get())
                 {
-                    if (auto* constrainer = editor->getConstrainer())
+                    if (canResize() == kResultFalse)
+                    {
+                        // Ableton Live will call checkSizeConstraint even if the view returns false
+                        // from canResize. Set the out param to an appropriate size for the editor
+                        // and return.
+                        auto constrainedRect = component->getLocalArea (editor, editor->getLocalBounds())
+                                                        .getSmallestIntegerContainer();
+
+                        *rectToCheck = convertFromHostBounds (*rectToCheck);
+                        rectToCheck->right  = rectToCheck->left + roundToInt (constrainedRect.getWidth());
+                        rectToCheck->bottom = rectToCheck->top  + roundToInt (constrainedRect.getHeight());
+                        *rectToCheck = convertToHostBounds (*rectToCheck);
+                    }
+                    else if (auto* constrainer = editor->getConstrainer())
                     {
                         *rectToCheck = convertFromHostBounds (*rectToCheck);