While Definition::getArgument() could be used to fetch replaced values, it relied upon bad comparison logic (e.g. "index_1" > 1). Additionally, storing original arguments and replacements in the same array makes Definition::getArguments()'s bounds check unreliable. A single argument and its replacement would count twice, allowing getArgument(2) to pass the bounds check and result in an array index error.
With this new method, fetching of replacement arguments is more straightforward and bounds checking functions as it should.
Previously, the Definition class was used both for type inference and factory construction (if factoryService was absent). This is fine for cases where classes create instances of themselves (e.g. getInstance() or create()), but leads to ambiguity when we have a separate factory class.
