1. Setting max LOD clamp = FLT_MAX via setSamplerState caused mipmap
  tests failure on Intel. It always picked wrong mipmap level during
  texture sampling. Fix: Use value from SamplerState::getMaxLod()
  instead.
2. Also set default linear filtering for blit shader's sampler.
  Previously there was no sampler set for this shader. It caused black
  fragments on Intel.

This CL is a prerequisite for enabling end2end tests on Intel & Metal.

Bug: angleproject:4133
Bug: angleproject:4915
Bug: angleproject:2634
Change-Id: I9e6b669712a294e09ab692a3c65f3956a799ef8b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2329089
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>