Feature: support midirealtimein for plugin transport

[dromer]

Something that seems missing right now is the ability to synchronize plugdata to the host transport using [midirealtimein] object.
Of course this is a kind of "emulation" since the plugin doesn't receive such midi messages from the host.

In Heavy we are using this with the DPF wrapper to simulate such transport events (atm requiring midi input on the generated plugin, but I want to refactor that so it is always present).

While we do have the [playhead] abstraction for timeline and transport data this doesn't receive any clock ticks. So being able to support [midirealtimein] for the plugins would definitely be handy.