The arrayOfStructsSize parameter can always be determined from the
TType object, so there's no need to pass it to
TType::createSamplerSymbols. Furthermore, it's more natural to do
the processing for arrays of structs in TType::createSamplerSymbols,
rather than in the TStructure::createSamplerSymbols helper it is
using.

Also rename some parameter names, and move createSamplerSymbols
implementation to Types.cpp.

This refactoring change prepares for implementing arrays of arrays.

BUG=angleproject:2125
TEST=angle_end2end_tests

Change-Id: I3f8bec711c0434677ebcf3741abb4f910c36dba3
Reviewed-on: https://chromium-review.googlesource.com/614883
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>