The reason I am doing this is that we have gotten reports about certain test
cases where we are emitting errors about self being captured in isolated
closures where the sourceloc is invalid. The reason why this happened is that
the decl returned by getIsolationCrossing did not have a SourceLoc since self
was being used implicitly.
In this commit I fix that issue by using SIL level information instead of AST
level information. This guarantees that we get an appropriate SourceLoc. As an
additional benefit, this fixed some extant errors where due to some sort of bug
in the AST, we were saying that a value was nonisolated when it was actor
isolated in some of the error msgs.
rdar://151955519
(cherry picked from commit f31236931b)
d6891a7395