[clang][bytecode] Can't revisit variables with invalid initializers

Consider:
```c++
struct T {
constexpr int get() const { return 5; }
};
const T &f(const T& t) { return t; }
const T &t = f(T());
static_assert(t.get() == 5);
```
https://godbolt.org/z/7139WMbEx

We revisit `t`, but the initializer is invalid (it's calling a non-constexpr function).

Even with https://github.com/llvm/llvm-project/pull/187918, this doesn't work yet.

Start with the reduced C++ example and reproduce it through the linked Godbolt case, then inspect Clang's bytecode handling for revisiting a variable whose initializer is invalid. Compare the behavior with the changes in PR 187918. Done means the example's static_assert succeeds without treating the non-constexpr initializer as valid.

Written by the indexing model from the issue text.