When the host creates an IContextMenu, the initial refcount should be 1 rather than zero.

Only include context observer block when workgroup types available.

This allows real-time threads to join an audio workgroup on Apple platforms.

Using a preferred channel config with no input or output channels could
cause an assertion here because the AudioProcessor will always have a
single input/output bus by default.

AudioProcessorParameterWithID pre-dates HostedAudioProcessorParameter,
which is why AudioProcessorParameterWithID was initially used for this
purpose.