implement realtime extension support: AAPXS SysEx8

[atsushieno]

As it has been written in several issues and documents (e.g. issue #73, issue #145, issue #158), current Binder-based extension() support does not cover realtime usage scenario and they should be covered as in MIDI2 system exclusive messages at process().

Now that we have refresh implementation for plugin manager with aap::MidiDestinationNode which is ready to be used in aap::PluginPlayer, it is time to actually implement it.

There are handful of blocks that need new code:

• [x] `PluginPlayer needs to provide users ways to handle its MIDI2 outputs, either via event handler or provide direct buffer to MIDI outputs.
• [x] cmidi2 needs sysex8 data extraction feature
• [x] implement MIDI2 AAPXS SysEx8 parser and generator
• [x] MIDI AAPXS service needs to parse MIDI2 sysex8 inputs into extension invocation, serialized as extension bytes.
• [x] aap::LocalPluginInstance needs to integrate this MIDI input parsing support.
• [x] MIDI AAPXS client needs to generate MIDI inputs from extension invocation, serialized as extension bytes. -> post-0.7.8 task
• [x] aap::RemotePluginInstance needs to integrate this MIDI output generation support.
• [x] the new plugin manager needs to implement realtime extension invocation. MIDI Program Change is a good example for this (involves preset setter).
• [x] There should be asynchronous callback support in every async-ified (non-RT) extension function, and they need to be invoked at each AAPXS implementation.
• [x] C++ wrappers in standard-extensions.h and its implementation also needs async-ification.

Unless it is going to be too complicated, it should be done before 0.7.8 release.

[atsushieno]

A few additional notes:

• a host that supports MIDI2 realtime extension needs to "copy" the parsed data into AAPXSServiceInstance, as the AAPXSServiceInstance might make use of the shared data within its context.
• likewise, the host would need to retrieve the "result" data AAPXSClientInstance shared memory.

[atsushieno]

Unless it is going to be too complicated, it should be done before 0.7.8 release.

As issues #171 is post-0.7.8 work, the entire work is inherently moved to post-0.7.8 as well. Until then, we will have proof-of-concept setPresetIndex() call at aap::AudioPluginNode::setPresetIndex(int index) to conditionally generate AAPXS SysEx8 and send it.

[atsushieno]

Most of the work is now done in aapxs-v080 branch, but I noticed that binder-client-as-plugin's get_extension() requires public extension API implementation for each AAPXS. It also needs to be provided by each AAPXS developer.

It is possible to achieve that by TypedAAPXS implementation classes, but that requires AAPXSDispatcher and its instantiated shared memory buffers, while AAPXSDefinition itself is basically all statically resolved. We likely need to provide another way to instantiate the registry, kind of.

[atsushieno]

^ is resolved as get_plugin_extension_proxy() member function in AAPXSDefinition.

[atsushieno]

We can close this issue once aapxs-v080 branch is merged to main.

[atsushieno]

It is now merged into main.