Improve collecting of referred symbols in memory_utils::get_symbols() by detecting sources of Loaded local raw pointers and references

[ironcev]

#5924 will remove collecting raw pointer and reference locals when collecting referred symbols. They are just intermediates and should not be collected as referred symbols.

This means, once #5924 is closed, we will not follow Loads anymore and will immediately bail out returning an ReferredSymbols::Incomplete result. This approach has the consequence of restricting/forbidding some optimizations even if they would be perfectly safe.

E.g., let's consider this example:

fn references(b: bool, ref_a: &mut u64, ref_b: &mut u64) {
    let x = 0;

    let ref_local = if b {
        ref_a
    } else {
        ref_b
    };

    *ref_local = 2;
}

The addresses are passed as arguments and we have no PtrToInts in the function. The *ref_local = 2; goes over typical IntToPtr -> Load chain that leads to ref_local. If we bail out here, we indicate to the rest of the analysis that we have an Incomplete information which will forbid further optimizations. Incomplete affects optimizations in a particular function and can fully restrict some like memcpyopt. The consequence in this example will be that the x = 0 does not get optimized away although it clearly can.

On the other hand, if we give best effort in detecting sources of ref_local, we will reach ref_a and ref_b in this case and come to a ReferredSymbols::Complete result. This will justify the safe removal of x = 0.

To conclude, giving best effort in following loaded_from in memory_utils::get_symbols() will remove non-existing constraints in optimizations.

Blocked by #5924.