MIDI only plugins are no longer provided valid audio buffers
Graph nodes are only executed when they have active connections

This change also allows the plugin to receive discrete layouts in hosts
that support them, while also maintaining support for
AudioChannelLayoutTags in Logic.

Previously, the child process could be deleted from its own
handleConnectionLost() callback, which would attempt to stop the child
process's thread from that same thread.

Now, the demo will attempt to stop the coordinator thread from the main
thread instead.

Some Windows 11 devices have both touch screens and mouse inputs, and
these can be used simultaneously.

The Viewport (and ListBox) now check the input source of each mouse
down. If the source is not a mouse, the viewport will always enter
drag-to-scroll mode, regardless of the result of isScrollOnDragEnabled.