Context should provide a one stop shop for symbol resolution

[dburgener]

symbol_in_context(), by design only resolves bound symbols. There's also TypeInfo;:typeinfo_from_string(), which turns a string into a TI, while performing "this" resolution, but not bound symbol lookup.

As a result, various call-sites for these seem to augment with various mixes of lookups.

We should create a new function in Context that does full resolution, including "this", bound symbols, aliases, and lookups in the global maps (both the Type and Function maps). Once that exists, caller sites can be converted to use it one by one.

This is too big a code change for pre-0.1, but something we should consider for the next major release after 0.1