swift234

[Sema] Add note to all unresolved witness types instead of just the first one. (#3458)

When issuing the error of "not conforming to a protocol P", we used to only note the first
unresolved witness type. This is inconsistent with the situation when the conformance
fails due to unimplemented functions, which we note all of the unimplemented functions.
This patch fixed this by noting all unresolved witness types.