Add modulation status to the param indication extension

[robbert-vdh]

The reasoning behind not doing this was that you could already tell that a parameter is being modulated by looking at the param modulation events. This is true if the parameter is currently being modulated, but there's no way to tell if a parameter has a modulation assignment if that modulation offset is currently zero. For consistency with the automation states, I think param indication should also have CLAP_PARAM_INDICATION_MODULATION_NONE and CLAP_PARAM_INDICATION_MODULATION_PRESENT flags.

[skei]

it could also be nice to know if a parameter is modulated mono- or polyphonically.. for mono, we could indicate the current value on the gui knob, but polyphonically (or via multiple modulators) it could make more sense to draw the range of modulation instead.. or in a different color, blue for mono/single, green for poly/multiple..