new loplugin: inlinesimpleaccessmethods

Create a rewriting plugin for finding methods that simply return
object fields, and should therefore be declared in the header,
so that the compiler can reduce method calls into a simple
fixed-offset load instruction.

Change-Id: I7a620fc54250b79681918dc31ed9a8f21118c037
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>