[516524] Use more efficient feature look-up in ReferenceUtil

ReferenceUtil could make use of an EClass.getFeatureID(feature) which
returns -1 if the feature doesn't belong to the class. Only in that case
do we need to try to look up the feature by name. Once we've computed
the feature ID, we can use it directly to efficiently access the
generated reflective methods.

This is a replacement of the reverted change 96871, as 96871 has been
reverted for an Oxygen release candidate build of EMF Compare.

Bug: 516524
Change-Id: I6ff031ebc02dd10bf3b0d88c00f03f15c25cfb62
Signed-off-by: Philip Langer <planger@eclipsesource.com>
2 files changed