Enable devirtualization for abstract and sub-class methods.

If we know the type of a receiver in the verifier we record devirtualization
data. Currently we only use this data to avoid virtual method dispatch when
we know the receiver of a method isn't a sub-class. This change allows
devirtualization of virtual and interface methods when we know the receiver's
type and the method the we'd find via dispatch is either known within boot or
has a reference from the current dex file.

Pass the receiver through to the method resolution trampoline as
devirtualization may mean the dex method index needs to be made more accurate
for the receiver.

Tidy up method devirtualization and related statistics.

Push the devirtualization map lookup into a less common case to avoid
taking its lock.

Make MethodReference a struct rather than a typedef of a pair, so the members
can have more meaningful names than first and second.

Rough statistics show that we devirtualize using this change around 2.5% of
the time, whilst some apps like GMS core devirtualize over 3.4% of the time.

Change-Id: Ieed3471dbedfc4cc881d652631b67176bb37d394