This commit replaces `Collections.unmodifiableList(Arrays.asList(array))`
with `new ImmutableArrayList<>(array)`, where `ImmutableArrayList` is
a simple implementation of an immutable array-backed list. This reduces
the number of allocations from 2 to 1 on many places in the code.

Additionally, this commit slightly improves javadoc of some methods
in the `AnnotationInstance` class.