Add support for sending Midi CCs out of VST3 plugins

[reuk]

VST3 plugins built with JUCE 6 will understand LegacyMidiCCOutEvents:

`juce6` technical preview branch

VST3 CC Improvements The VST3 wrapper has been taught to understand a wider variety of Vst::Event types. In particular, it now understands the kLegacyMIDICCOutEvent type, meaning that VST3 plugins can send and receive MIDI CC messages, as well as channel-pressure, pitch-bend, program-change, quarter-frame, and poly-pressure messages. It also fixes an issue where the kPolyPressureEvent was incorrectly being converted to a channel pressure MIDI message. Now, kPolyPressureEvents will be conve…