Rework of Execution context setting per operation

[Leo-Besancon]

Currently, the execution context is persistant during a slot execution, but relies on a lot of reset logic per each execution (of an operation, async_message or deferred_call.
As a result, we have to ensure that each field is correctly reset at the beginning of an execution:

• gas_remaining_before_subexecution
• recursion_counter
• stack
• user_event_count_in_current_exec
• ...

It is error prone, as forgetting setting it at one place can have heavy consequences (e.g. see checklist here: #4840 (comment))

We should group all these fields in a single struct (e.g. OperationContext), so that we can reset everything at once.