Refactor augment generator linkage

Refactor augment generator linkage

The uses/augment and module/augment cases are quite different from
the perspective how we map their argument reference to generators.

The uses/augment case is quite simple, as it refers to grouping's nodes,
not augmentations. The only variation we need to account for is the
skip back to the defining grouping.

The module/augment case, on the other hand, is more complex, as it can
refer to augmentations -- hence it need to account for changes namespace
changes along uses/grouping as well as back from grouping child to
augmentations.

JIRA: MDSAL-715
Change-Id: I7425301afa6de566d985d19450ccfc64ea527119
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>