[Serialization] Reword xref errors and show notes for common issues#36431

Merged

xymus merged 3 commits intoswiftlang:mainfrom

xymus:notes-on-xrefs

Mar 19, 2021

Commits on Mar 18, 2021

[Serialization] Add notes to XRef errors for common failures
xymus
committed
[Serialization] Try to improve readability of a common deserialization failures
xymus
committed
[Serialization] Test the output on a crash due to a broken XRef
xymus
committed