Resolve constants inside IDL definitions

[quic-nhaas]

Any array or constant can only be defined with an integer literal. The request is to allow using constants defined in the IDL as integers.
For example:

/** Max number of keys that the cache can store. */
const uint32 MAX_KEYS = 24;

struct Cache {
  uint32 numKeys; /** Size the cache. */
  MyKey[MAX_KEYS] keyInfo; /** Info about type of keys available to store/get. */
};

interface IFoo {
  method foo (out Cache cache);
};