[gl] Skip sendVertexAttributes if no client arrays

bug: 143919384

+ Cache the enabled/clientarray state

Test: dEQP-GLES2/3 no regressions
Test: webgl aquarium 20k fishes: 27-29 fps to 31-35 fps

Change-Id: Icf01f2187b6331818926d7806a0ba2e75e0aeb67
3 files changed