[dyld cache] Support dylibs trie

[p-x9]

Dylibs trie is for searching by dylib name.
Aliases are also supported, with identical ones returning the same index.

This index matches the index in the dylib image list that can be retrieved from imagesOffset.

uint64_t    dylibsTrieAddr;         // (unslid) address of trie of indexes of all cached dylibs
uint64_t    dylibsTrieSize;         // size of trie of cached dylib paths

dylibsTrieAddr is set to 0 outside the main cache, but the actual content may exist in the sub-cache.