Add a new struct spa_param_info that lists the available params on
a node/port and if they are readable/writable/updated. We can use
this to replace and improve the PARAM_List and also to notify
property change and updates.
Update elements and code to deal with this new param stuff. Add
port and node info to most elements and signal changes.
Use async enum_params in -inspect and use the param info to know
which ones to enumerate.
Use the port info to know what parameters to update in the
remote-node.
Only allow properties inside objects, this makes it easier to
iterate the object, which is needed for efficiently processing
control streams.
Add a choice type to mark variable properties.
SPA_TYPE_Enum -> SPA_TYPE_Id to avoid confusion with choice enum
Make it easier to allocate and initialize properties on the stack
Make more efficient methods to make objects.
Add control properties to audiotestsrc for frequency and volume
and add a test program.
Add size parameter to set_io for additional checks and to make it
easy to know how much control data we can write.
