This restores the functionality of JUCE_COREGRAPHICS_RENDER_WITH_MULTIPLE_PAINT_CALLS.
Using this preprocessor flag may avoid Core Graphics rendering much larger regions than
necessary, but the small regions that are rendered will likely be rendered slower.
Whether using this flag improves or degrades the performance of your rendering overall
will be specific to each application.

Previously enabling JUCE_COREGRAPHICS_RENDER_WITH_MULTIPLE_PAINT_CALLS was ineffective
from versions of macOS around 10.13, but enabling it didn't have any negative impact on
performance. Now enabling JUCE_COREGRAPHICS_RENDER_WITH_MULTIPLE_PAINT_CALLS may result
in slower rendering.

This change adds the examples from `examples/Plugins` to the
AudioPluginHost, surfacing them as 'internal' plugins in the popup menu.