Assigning the selector of a parent function to a constant crashes solc

This Solidity:

```Solidity
contract B {
function g() public {}
}

contract C is B {
// the constant keyword triggers the crash
bytes4 public constant s2 = B.g.selector;
}
```

crashes the compiler with the following error:

```
❯ solc --version
solc, the solidity compiler commandline interface
Version: 0.8.30+commit.73712a01.Linux.g++
❯ solc --ir reproducer.sol
Uncaught exception:
Dynamic exception type: std::out_of_range
std::exception::what: map::at
```

Start by compiling the supplied reproducer with solc 0.8.30 and the --ir option, confirming the std::out_of_range map::at crash. Trace the compiler path handling a parent function selector in a constant initializer; done means the example compiles without crashing and has a regression test covering this case.

Written by the indexing model from the issue text.