Rewrite phutil symbol management to be more sane and not leave random dangling __functions() all over the place.
Summary: All loading/query functionality now lives in PhutilSymbolLoader, and
phutil_libraryinit.php is not so crazy anymore. PhutilSymbolLoader provides
a reasonable "query object" interface to the symbol tables, instead of having
one-off functions for every type of query.
Test Plan:
Reviewers:
CC: