Expose immediate base contracts for each contract

[Xenomega]

Currently slither API provides contract.inheritance which refers to linearized base contracts (a flattened list of the inheritance hierarchy). This requests support for the immediate base contracts inherited from for any given contract.

For example:

contract A {
    // ...
}

contract B is A {
    // ...
}

contract C is A {
    // ...
}

contract D is B, C {
    // ...
}

I would like to be able to determine that the base contracts for D are B, C (in order, even if reversed), where as linearized base contracts would yield C, B, A