Use pre-sized ImmutableLists for yang-data-api

Use pre-sized ImmutableLists for yang-data-api

ImmutableList.builder() did not pre-size its arrays correctly,
leading to poor performance. That is no longer the case and we can
correctly pre-allocate it -- giving us the ArrayList equivalent in
immutable form, hence skipping copying in
{SchemaPath,YangInstanceIdentifier}.create()

Change-Id: I4a070dca26138f28de69e4a0e1f9b0298ee2312b
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit da9ee8c80328bd6e21064e44f95f29ffc1e99d41)