func_adapter: use ports for arguments and return values

Current func_adapter implementation has several drawbacks. Firstly, the
interface has 21 virtual method (except for virtual destructor) which
means you need to implement all these methods if you need a new
func_adapter. Secondly, if you need to pass arguments from Lua to
func_adapter, you need to iterate over Lua stack and push the value to
func_adapter with appropriate type.

We have internal interface for calling persistent functions - port.
Let's use it for triggers too. It will allow to easily implement new
func_adapter since it will have only call method and virtual destructor.
Also, it will allow to easily call any func_adapter from Lua using
port_lua - now module trigger relies on the fact that there are only Lua
triggers. This change reduces code complexity as well - since we are
using port_c for triggers, that allows to be dumped several times, we
can create helper `event_run_triggers` which incapsulates work with
`event_trigger_iterator` and simply calls all the triggers from the
event passing the same port with arguments.

Since func_adapter is used mostly for triggers, let's make both ports
arguments optional - many triggers have no arguments and almost all
triggers ignore returned values.

Along the way, fix a possible crash when iterator passed to
transactional trigger is saved and used after the trigger is over.

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