Support aggregating generators for classically dynamic callable selection

When an exact callable is a result of a classically dynamic selection, RCA doesn't know which callable generator to use and can't perform further analysis. For example:
```qsharp
let cond = true;
let f = if cond { op1 } else { op2 };
f()
```
Even though the condition is a compile time constant, this might be across longer calculation that makes it non-obvious which callable will be invoked on the last line. To handle this, RCA would need some fairly complex mechanism for aggregating across arbitrary code the resulting generators to use the sum of the dynamism. Note that a single if-statement might be easy, but they can be arbitrarily nested, call functions that return callables, or select callables from within an array, so while this aggregation should be possible it is not straightforward.