We need to always call reset() during createPipelineLayout(),
particularly to reset the descriptor pools to handle the new descriptor
set layouts that are generated by new immutable samplers. Otherwise,
DynamicDescriptorPool::init() will detect that a pool is attempting to
be created with a mis-matching descriptor set layout handle.

Bug: angleproject:4307
Test: Manually verify Cut the Rope doesn't crash
Change-Id: I0993bc37170e3ddf45c50abdfefda1d7f782b801
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2441127Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Tim Van Patten <timvp@google.com>