Update binding-dom adaptation to remove AugmentationNode

Update binding-dom adaptation to remove AugmentationNode

AugmentationIdentifier and AugmentationNode are being removed from
yang-data-api.

This patch adapts mdsal-binding-dom-codec to reflect the
fact Augmentation no longer has one-to-one equivalent. This means that
users need to check whether the code tree node refers to an Augmentation
or to a regular DataObject.

One particular sore point is that toNormalized() can no longer return a
plain Entry of NormalizedNode, as Augmentations do not have a backing.
To solve this, we introduce NormalizedResult with two specializations,
NodeResult and AugmentationResult.

In order to deal with DTCL changes, we also memoize
dataBefore/dataAfter, as it guides LazyAugmentationModification's
correct identification whether the a node has appeared, was modified, or
disappeared.

JIRA: MDSAL-820
Change-Id: I0360fd8f74ddb6df82ba64f7a87f6d92ce855162
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>