releng: Transition to jdt.annotation 2.0

releng: Transition to jdt.annotation 2.0

The new o.e.jdt.annotation 2.0 annotations (based on Java 8
Type Annotations [1]) can now apply on generic type declarations,
allowing things like "List<@NonNull String>".

The @NonNullByDefault annotation, already in use, will now apply
to these locations. This required some code changes to eliminate
compilation errors, notably in places where null checks were
previously made and were not needed, or where some existing
declarations had to be specified as @Nullable.

Another relatively important change is the new syntax for []
arrays. Before, only "@NonNull String[]" was allowed, which meant
"a non-null reference to an array of unspecified Strings". Now, it
instead means "an unspecified reference to an array of non-null
Strings".

It is still possible to specify the array reference itself, but by
doing: "String @NonNull []". Both locations can be annotated
independently.

[1] See https://docs.oracle.com/javase/tutorial/java/annotations/type_annotations.html

Change-Id: I4cb0a3266928c24cfd7f8ed442c93556132f892c
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/57252
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>