Non-thread-safe access in synchronized Results class in DependencyCollectorDelegate #1995

Affected version: HEAD

File: maven-resolver-impl/src/main/java/org/eclipse/aether/internal/impl/collect/DependencyCollectorDelegate.java:571-598

addException() and addCycle() are synchronized on Results, but they call result.getExceptions() and result.getCycles() on a CollectResult that may not be thread-safe. If CollectResult's internal collections are not synchronized or safely published, concurrent modifications may not be visible.

Originally reported in #1944.