Updates the message to use the type or ValueDecl instead of this on previous 'Found this candidate' messages
Note: doees not yet change all test cases so more tests are failing
Improve Diagnostic message on overload ambiguitiy
Remove messages that say 'found this candidate' in favour of providing the type for the candidate to aid in selection when the candidates are presented in a dialogue window.
Fix more tests
Tweaked usable check:
* Local type/func decls are usable even before declaration
* Outer nominal Instance member are not usable
* Type context cannot close over values in outer type contexts
Added shadowing rule by the base name:
* Type members don't shadow each other as long as they are in the
same type context.
* Local values shadow everything in outer scope
* Except that 'func' decl doesn't shadow 'var' decl if they are in the
same scope.
rdar://86285396
