There was a problem with `reportDiagnosticOnce` method which was
called, for example, to report diagnostics about experimentalities. It
was crucial for code as in the issue (KT-34204).
The whole complexity was "count of experimental diagnostics" multiply
"count of all diagnostics" multiply very large constant. Almost on
each `reportDiagnosticOnce` method `readonlyView()` was called which
in turn called computation of cache. During cache computation we were
iterating through the all diagnostics and also were using
KotlinSuppressCache, which is not very fast.
#KT-34204 Fixed
Mikhail Zarechenskiy
3d8e5c4f8e