Implement std::consteval_hash<std::meta::info>

[fullptr]

Implements https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3816r0.html in a way that is stable across repeated runs of the compiler on unchanged source code.

The simplest way to define the hash is to just hash the AST pointer that the given reflection represents, but this results in different hash values with each compilation run which is undesirable (the compiler should not introduce sources of instability, repeated compilations should yield the same result).

This implementation instead looks at what the reflection represents underneath and constructs a hash based on the value, resulting in hash values that are stable across repeated runs. Creating hashes for types in this way proved trickier, so this PR instead assigns a unique value to every type which gets for its hash value instead. These are defined in the order that the types are, so rearranging types in the source code can change the values, but they remain stable across repeat builds.

The obvious downside with this approach is that it needs to be updated whenever future standards introduce new constructs that can be reflected. A second approach can be found here which uses a way to generate a stable value from the underlying pointer AST which makes the implementation much simpler and does not need to be continuously updated with future standards.