Instead of storing instance names as part of TInterfaceBlock, store
instance names only in interface block instance symbols. Wherever the
instance name is needed it can be fetched from the instance symbol.

BUG=angleproject:2267
TEST=angle_end2end_tests

Change-Id: Ia265e4db7901eebec57c9c3769d84c17651a35ba
Reviewed-on: https://chromium-review.googlesource.com/803221Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>