GLES2: sequence operator (,) eval order and side effects

GLES2: sequence operator (,) eval order and side effects

Ported from:
https://github.com/KhronosGroup/WebGL/blob/master/sdk/tests/conformance/glsl/bugs/sequence-operator-evaluation-order.html
Which was added in:
https://github.com/KhronosGroup/WebGL/pull/981
https://github.com/KhronosGroup/WebGL/pull/1932

These tests were known to fail in on Pixel 2016 / Android 7.1.1.

New tests:
  dEQP-GLES2.functional.shaders.operator.sequence.side_effects.affect_ternary
  dEQP-GLES2.functional.shaders.operator.sequence.side_effects.affect_and
  dEQP-GLES2.functional.shaders.operator.sequence.side_effects.affect_or
Components: AOSP

Change-Id: I7bbcaecc08279df6f30b6855cc99b19b402892c7