Execute transactions inline [#3184]

Closes #3184 (closed). Executes transactions inline within the message executor, such as the signature executor, or synthetic message executor, instead of queuing transactions for execution later in Block.Process.

Also stops reordering messages to put transactions last, because now the order doesn't matter. When executed bare (not nested) the transaction executor just records the transaction, and the signature executor can find the transaction in the message bundle the transaction does not need to be recorded first.

Changelog: refactor