Index getter methods by String

Index 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.

JIRA: MDSAL-398
Change-Id: I36526ce15735d4ef8e4ba847bcc24ea69b950e94
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit 4c0eb46c1924ca71bb4092b0c91fceb5b790e3f8)