Index nonnull/getter methods by String

Index nonnull/getter methods by String

Looking up by String offers slight advantage over Method lookup,
because we'll end up with a constant hashCode() over objects which
are guaranteed to be interned.

This rework implies we no longer get to have a map whose keySet
reflects property methods -- which is fine, as the keyset would
take up more memory than a plain array, so we retain the methods
in an array -- hence this ends up being a net win in both cases.

Furthermore it flushes out the fact that nonnull methods should
not really cache their result -- for example if the user performs
a nonnull() access and then runs hashCode(), we'll end up performing
two decodes, as nonnull() cache will not be picked up by hashCode().

We therefore construct nonnull->getter String map, which we consult
on nonnull accesses and only wrap it without caching. This has
the benefit of keeping the cache smaller while maintaining its
effectiveness.

JIRA: MDSAL-398
Change-Id: I36526ce15735d4ef8e4ba847bcc24ea69b950e94
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>