Rework IPC declaration syntax

[neobrain]

The IPC platform definitions in source/platform are super useful, but they were implemented at a time were C++ metaprogramming was highly limiting. With C++20, a much simpler and faster-to-compile syntax could be adopted. Furthermore, per-parameter description texts could be added (for integration in debug traces).

I'm thinking of something like this:

// Previously:
// using DeleteDirectory = IPC::IPCCommand<0x806>::add_uint32::add_uint64::add_uint32::add_uint32::add_static_buffer::response;

// New:
inline constexpr auto DeleteDirectory = IPCCommand(
    AddU32("Transaction", "Transaction parameter description"),
    AddSerialized<ArchiveHandle>("Archive handle", "Handle for the archive the directory belongs to"),
    AddSerialized<Path>("Path", "Directory path"),
    ...
    );
};