Revise the documentation on how multiple symbols at the same address are handled

To avoid non-determinism and provide consistent behavior in all cases,
now only confidence, symbol type, and name are considered when
disambiguating multiple symbols at the same address.

The previously documented behavior was not what was implemented. While
recency was considered in some cases for disambiguating symbols at the
same address, respecting it consistetly results in non-deterministic
behavior when symbols are being added concurrently by multiple sources.